Command-line API | Node.js v24.14.1 Documentation

Skip to content
Table of contents

- Command-line API
  - Synopsis
  - Program entry point
  - Options
    - `-`
    - `--`
    - `--abort-on-uncaught-exception`
    - `--allow-addons`
    - `--allow-child-process`
    - `--allow-fs-read`
    - `--allow-fs-write`
    - `--allow-inspector`
    - `--allow-wasi`
    - `--allow-worker`
    - `--build-snapshot`
    - `--build-snapshot-config`
    - `-c`, `--check`
    - `--completion-bash`
    - `-C condition`, `--conditions=condition`
    - `--cpu-prof`
    - `--cpu-prof-dir`
    - `--cpu-prof-interval`
    - `--cpu-prof-name`
    - `--diagnostic-dir=directory`
    - `--disable-proto=mode`
    - `--disable-sigusr1`
    - `--disable-warning=code-or-type`
    - `--disable-wasm-trap-handler`
    - `--disallow-code-generation-from-strings`
    - `--dns-result-order=order`
    - `--enable-fips`
    - `--enable-network-family-autoselection`
    - `--enable-source-maps`
    - `--entry-url`
    - `--env-file-if-exists=file`
    - `--env-file=file`
    - `-e`, `--eval "script"`
    - `--experimental-addon-modules`
    - `--experimental-config-file=config`
    - `--experimental-default-config-file`
    - `--experimental-eventsource`
    - `--experimental-import-meta-resolve`
    - `--experimental-inspector-network-resource`
    - `--experimental-loader=module`
    - `--experimental-network-inspection`
    - `--experimental-print-required-tla`
    - `--experimental-require-module`
    - `--experimental-sea-config`
    - `--experimental-shadow-realm`
    - `--experimental-test-coverage`
    - `--experimental-test-module-mocks`
    - `--experimental-transform-types`
    - `--experimental-vm-modules`
    - `--experimental-wasi-unstable-preview1`
    - `--experimental-webstorage`
    - `--experimental-worker-inspection`
    - `--expose-gc`
    - `--force-context-aware`
    - `--force-fips`
    - `--force-node-api-uncaught-exceptions-policy`
    - `--frozen-intrinsics`
    - `--heap-prof`
    - `--heap-prof-dir`
    - `--heap-prof-interval`
    - `--heap-prof-name`
    - `--heapsnapshot-near-heap-limit=max_count`
    - `--heapsnapshot-signal=signal`
    - `-h`, `--help`
    - `--icu-data-dir=file`
    - `--import=module`
    - `--input-type=type`
    - `--insecure-http-parser`
    - `--inspect-brk[=[host:]port]`
    - `--inspect-port=[host:]port`
    - `--inspect-publish-uid=stderr,http`
    - `--inspect-wait[=[host:]port]`
    - `--inspect[=[host:]port]`
      - Warning: binding inspector to a public IP:port combination is insecure
    - `-i`, `--interactive`
    - `--jitless`
    - `--localstorage-file=file`
    - `--max-http-header-size=size`
    - `--max-old-space-size-percentage=percentage`
    - `--napi-modules`
    - `--network-family-autoselection-attempt-timeout`
    - `--no-addons`
    - `--no-async-context-frame`
    - `--no-deprecation`
    - `--no-experimental-detect-module`
    - `--no-experimental-global-navigator`
    - `--no-experimental-repl-await`
    - `--no-experimental-require-module`
    - `--no-experimental-sqlite`
    - `--no-experimental-websocket`
    - `--no-extra-info-on-fatal-exception`
    - `--no-force-async-hooks-checks`
    - `--no-global-search-paths`
    - `--no-network-family-autoselection`
    - `--no-strip-types`
    - `--no-warnings`
    - `--node-memory-debug`
    - `--openssl-config=file`
    - `--openssl-legacy-provider`
    - `--openssl-shared-config`
    - `--pending-deprecation`
    - `--permission`
    - `--preserve-symlinks`
    - `--preserve-symlinks-main`
    - `-p`, `--print "script"`
    - `--prof`
    - `--prof-process`
    - `--redirect-warnings=file`
    - `--report-compact`
    - `--report-dir=directory`, `report-directory=directory`
    - `--report-exclude-env`
    - `--report-exclude-network`
    - `--report-filename=filename`
    - `--report-on-fatalerror`
    - `--report-on-signal`
    - `--report-signal=signal`
    - `--report-uncaught-exception`
    - `-r`, `--require module`
    - `--run`
      - Intentional limitations
      - Environment variables
    - `--secure-heap-min=n`
    - `--secure-heap=n`
    - `--snapshot-blob=path`
    - `--test`
    - `--test-concurrency`
    - `--test-coverage-branches=threshold`
    - `--test-coverage-exclude`
    - `--test-coverage-functions=threshold`
    - `--test-coverage-include`
    - `--test-coverage-lines=threshold`
    - `--test-force-exit`
    - `--test-global-setup=module`
    - `--test-isolation=mode`
    - `--test-name-pattern`
    - `--test-only`
    - `--test-reporter`
    - `--test-reporter-destination`
    - `--test-rerun-failures`
    - `--test-shard`
    - `--test-skip-pattern`
    - `--test-timeout`
    - `--test-update-snapshots`
    - `--throw-deprecation`
    - `--title=title`
    - `--tls-cipher-list=list`
    - `--tls-keylog=file`
    - `--tls-max-v1.2`
    - `--tls-max-v1.3`
    - `--tls-min-v1.0`
    - `--tls-min-v1.1`
    - `--tls-min-v1.2`
    - `--tls-min-v1.3`
    - `--trace-deprecation`
    - `--trace-env`
    - `--trace-env-js-stack`
    - `--trace-env-native-stack`
    - `--trace-event-categories`
    - `--trace-event-file-pattern`
    - `--trace-events-enabled`
    - `--trace-exit`
    - `--trace-require-module=mode`
    - `--trace-sigint`
    - `--trace-sync-io`
    - `--trace-tls`
    - `--trace-uncaught`
    - `--trace-warnings`
    - `--track-heap-objects`
    - `--unhandled-rejections=mode`
    - `--use-bundled-ca`, `--use-openssl-ca`
    - `--use-env-proxy`
    - `--use-largepages=mode`
    - `--use-system-ca`
    - `--v8-options`
    - `--v8-pool-size=num`
    - `-v`, `--version`
    - `--watch`
    - `--watch-kill-signal`
    - `--watch-path`
    - `--watch-preserve-output`
    - `--zero-fill-buffers`
  - Environment variables
    - `FORCE_COLOR=[1, 2, 3]`
    - `NODE_COMPILE_CACHE=dir`
    - `NODE_COMPILE_CACHE_PORTABLE=1`
    - `NODE_DEBUG=module[,…]`
    - `NODE_DEBUG_NATIVE=module[,…]`
    - `NODE_DISABLE_COLORS=1`
    - `NODE_DISABLE_COMPILE_CACHE=1`
    - `NODE_EXTRA_CA_CERTS=file`
    - `NODE_ICU_DATA=file`
    - `NODE_NO_WARNINGS=1`
    - `NODE_OPTIONS=options...`
    - `NODE_PATH=path[:…]`
    - `NODE_PENDING_DEPRECATION=1`
    - `NODE_PENDING_PIPE_INSTANCES=instances`
    - `NODE_PRESERVE_SYMLINKS=1`
    - `NODE_REDIRECT_WARNINGS=file`
    - `NODE_REPL_EXTERNAL_MODULE=file`
    - `NODE_REPL_HISTORY=file`
    - `NODE_SKIP_PLATFORM_CHECK=value`
    - `NODE_TEST_CONTEXT=value`
    - `NODE_TLS_REJECT_UNAUTHORIZED=value`
    - `NODE_USE_ENV_PROXY=1`
    - `NODE_USE_SYSTEM_CA=1`
    - `NODE_V8_COVERAGE=dir`
      - Coverage output
      - Source map cache
    - `NO_COLOR=<any>`
    - `OPENSSL_CONF=file`
    - `SSL_CERT_DIR=dir`
    - `SSL_CERT_FILE=file`
    - `TZ`
    - `UV_THREADPOOL_SIZE=size`
  - Useful V8 options
    - `--abort-on-uncaught-exception`
    - `--disallow-code-generation-from-strings`
    - `--enable-etw-stack-walking`
    - `--expose-gc`
    - `--harmony-shadow-realm`
    - `--heap-snapshot-on-oom`
    - `--interpreted-frames-native-stack`
    - `--jitless`
    - `--max-old-space-size=SIZE` (in MiB)
    - `--max-semi-space-size=SIZE` (in MiB)
    - `--perf-basic-prof`
    - `--perf-basic-prof-only-functions`
    - `--perf-prof`
    - `--perf-prof-unwinding-info`
    - `--prof`
    - `--security-revert`
    - `--stack-trace-limit=limit`

## Command-line API#

Node.js comes with a variety of CLI options. These options expose built-in debugging, multiple ways to execute scripts, and other helpful runtime options.

To view this documentation as a manual page in a terminal, run `man node`.

### Synopsis#

`node [options] [V8 options] [<program-entry-point> | -e "script" | -] [--] [arguments]`

`node inspect [<program-entry-point> | -e "script" | <host>:<port>] …`

`node --v8-options`

Execute without arguments to start the REPL.

For more info about `node inspect`, see the debugger documentation.

### Program entry point#

The program entry point is a specifier-like string. If the string is not an absolute path, it's resolved as a relative path from the current working directory. That entry point string is then resolved as if it's been requested by `require()` from the current working directory. If no corresponding file is found, an error is thrown.

By default, the resolved path is also loaded as if it's been requested by `require()`, unless one of the conditions below apply—then it's loaded as if it's been requested by `import()`:

- The program was started with a command-line flag that forces the entry point to be loaded with ECMAScript module loader, such as `--import`.
- The file has an `.mjs`, `.mts` or `.wasm` extension.
- The file does not have a `.cjs` extension, and the nearest parent `package.json` file contains a top-level `"type"` field with a value of `"module"`.

See module resolution and loading for more details.

### Options#

History

Version | Changes
--- | ---
v10.12.0 | Underscores instead of dashes are now allowed for Node.js options as well, in addition to V8 options.

Stability: 2 - Stable

All options, including V8 options, allow words to be separated by both dashes (`-`) or underscores (`_`). For example, `--pending-deprecation` is equivalent to `--pending_deprecation`.

If an option that takes a single value (such as `--max-http-header-size`) is passed more than once, then the last passed value is used. Options from the command line take precedence over options passed through the `NODE_OPTIONS` environment variable.

#### `-`#

Added in: v8.0.0

Alias for stdin. Analogous to the use of `-` in other command-line utilities, meaning that the script is read from stdin, and the rest of the options are passed to that script.

#### `--`#

Added in: v6.11.0

Indicate the end of node options. Pass the rest of the arguments to the script. If no script filename or eval/print script is supplied prior to this, then the next argument is used as a script filename.

#### `--abort-on-uncaught-exception`#

Added in: v0.10.8

Aborting instead of exiting causes a core file to be generated for post-mortem analysis using a debugger (such as `lldb`, `gdb`, and `mdb`).

If this flag is passed, the behavior can still be set to not abort through `process.setUncaughtExceptionCaptureCallback()` (and through usage of the `node:domain` module that uses it).

#### `--allow-addons`#

Added in: v21.6.0, v20.12.0

Stability: 1.1 - Active development

When using the Permission Model, the process will not be able to use native addons by default. Attempts to do so will throw an `ERR_DLOPEN_DISABLED` unless the user explicitly passes the `--allow-addons` flag when starting Node.js.

Example:

    // Attempt to require an native addon
    require('nodejs-addon-example');

    $ node --permission --allow-fs-read=* index.js
    node:internal/modules/cjs/loader:1319
      return process.dlopen(module, path.toNamespacedPath(filename));
                     ^

    Error: Cannot load native addon because loading addons is disabled.
        at Module._extensions..node (node:internal/modules/cjs/loader:1319:18)
        at Module.load (node:internal/modules/cjs/loader:1091:32)
        at Module._load (node:internal/modules/cjs/loader:938:12)
        at Module.require (node:internal/modules/cjs/loader:1115:19)
        at require (node:internal/modules/helpers:130:18)
        at Object.<anonymous> (/home/index.js:1:15)
        at Module._compile (node:internal/modules/cjs/loader:1233:14)
        at Module._extensions..js (node:internal/modules/cjs/loader:1287:10)
        at Module.load (node:internal/modules/cjs/loader:1091:32)
        at Module._load (node:internal/modules/cjs/loader:938:12) {
      code: 'ERR_DLOPEN_DISABLED'
    }

#### `--allow-child-process`#

History

Version | Changes
--- | ---
v24.4.0 | When spawning process with the permission model enabled. The flags are inherit to the child Node.js process through NODE_OPTIONS environment variable.
v20.0.0 | Added in: v20.0.0

Stability: 1.1 - Active development

When using the Permission Model, the process will not be able to spawn any child process by default. Attempts to do so will throw an `ERR_ACCESS_DENIED` unless the user explicitly passes the `--allow-child-process` flag when starting Node.js.

Example:

    const childProcess = require('node:child_process');
    // Attempt to bypass the permission
    childProcess.spawn('node', ['-e', 'require("fs").writeFileSync("/new-file", "example")']);

    $ node --permission --allow-fs-read=* index.js
    node:internal/child_process:388
      const err = this._handle.spawn(options);
                               ^
    Error: Access to this API has been restricted
        at ChildProcess.spawn (node:internal/child_process:388:28)
        at node:internal/main/run_main_module:17:47 {
      code: 'ERR_ACCESS_DENIED',
      permission: 'ChildProcess'
    }

The `child_process.fork()` API inherits the execution arguments from the parent process. This means that if Node.js is started with the Permission Model enabled and the `--allow-child-process` flag is set, any child process created using `child_process.fork()` will automatically receive all relevant Permission Model flags.

This behavior also applies to `child_process.spawn()`, but in that case, the flags are propagated via the `NODE_OPTIONS` environment variable rather than directly through the process arguments.

#### `--allow-fs-read`#

History

Version | Changes
--- | ---
v24.2.0 | Entrypoints of your application are allowed to be read implicitly.
v23.5.0, v22.13.0 | Permission Model and --allow-fs flags are stable.
v20.7.0 | Paths delimited by comma (`,`) are no longer allowed.
v20.0.0 | Added in: v20.0.0

This flag configures file system read permissions using the Permission Model.

The valid arguments for the `--allow-fs-read` flag are:

- `*` - To allow all `FileSystemRead` operations.
- Multiple paths can be allowed using multiple `--allow-fs-read` flags. Example `--allow-fs-read=/folder1/ --allow-fs-read=/folder1/`

Examples can be found in the File System Permissions documentation.

The initializer module and custom `--require` modules has a implicit read permission.

    $ node --permission -r custom-require.js -r custom-require-2.js index.js

- The `custom-require.js`, `custom-require-2.js`, and `index.js` will be by default in the allowed read list.

    process.has('fs.read', 'index.js'); // true
    process.has('fs.read', 'custom-require.js'); // true
    process.has('fs.read', 'custom-require-2.js'); // true

#### `--allow-fs-write`#

History

Version | Changes
--- | ---
v23.5.0, v22.13.0 | Permission Model and --allow-fs flags are stable.
v20.7.0 | Paths delimited by comma (`,`) are no longer allowed.
v20.0.0 | Added in: v20.0.0

This flag configures file system write permissions using the Permission Model.

The valid arguments for the `--allow-fs-write` flag are:

- `*` - To allow all `FileSystemWrite` operations.
- Multiple paths can be allowed using multiple `--allow-fs-write` flags. Example `--allow-fs-write=/folder1/ --allow-fs-write=/folder1/`

Paths delimited by comma (`,`) are no longer allowed. When passing a single flag with a comma a warning will be displayed.

Examples can be found in the File System Permissions documentation.

#### `--allow-inspector`#

Added in: v24.12.0

Stability: 1.0 - Early development

When using the Permission Model, the process will not be able to connect through inspector protocol.

Attempts to do so will throw an `ERR_ACCESS_DENIED` unless the user explicitly passes the `--allow-inspector` flag when starting Node.js.

Example:

    const { Session } = require('node:inspector/promises');

    const session = new Session();
    session.connect();

    $ node --permission index.js
    Error: connect ERR_ACCESS_DENIED Access to this API has been restricted. Use --allow-inspector to manage permissions.
      code: 'ERR_ACCESS_DENIED',
    }

#### `--allow-wasi`#

Added in: v22.3.0, v20.16.0

Stability: 1.1 - Active development

When using the Permission Model, the process will not be capable of creating any WASI instances by default. For security reasons, the call will throw an `ERR_ACCESS_DENIED` unless the user explicitly passes the flag `--allow-wasi` in the main Node.js process.

Example:

    const { WASI } = require('node:wasi');
    // Attempt to bypass the permission
    new WASI({
      version: 'preview1',
      // Attempt to mount the whole filesystem
      preopens: {
        '/': '/',
      },
    });

    $ node --permission --allow-fs-read=* index.js

    Error: Access to this API has been restricted
        at node:internal/main/run_main_module:30:49 {
      code: 'ERR_ACCESS_DENIED',
      permission: 'WASI',
    }

#### `--allow-worker`#

Added in: v20.0.0

Stability: 1.1 - Active development

When using the Permission Model, the process will not be able to create any worker threads by default. For security reasons, the call will throw an `ERR_ACCESS_DENIED` unless the user explicitly pass the flag `--allow-worker` in the main Node.js process.

Example:

    const { Worker } = require('node:worker_threads');
    // Attempt to bypass the permission
    new Worker(__filename);

    $ node --permission --allow-fs-read=* index.js

    Error: Access to this API has been restricted
        at node:internal/main/run_main_module:17:47 {
      code: 'ERR_ACCESS_DENIED',
      permission: 'WorkerThreads'
    }

#### `--build-snapshot`#

History

Version | Changes
--- | ---
v24.13.1 | The snapshot building process is no longer experimental.
v18.8.0 | Added in: v18.8.0

Generates a snapshot blob when the process exits and writes it to disk, which can be loaded later with `--snapshot-blob`.

When building the snapshot, if `--snapshot-blob` is not specified, the generated blob will be written, by default, to `snapshot.blob` in the current working directory. Otherwise it will be written to the path specified by `--snapshot-blob`.

    $ echo "globalThis.foo = 'I am from the snapshot'" > snapshot.js

    # Run snapshot.js to initialize the application and snapshot the
    # state of it into snapshot.blob.
    $ node --snapshot-blob snapshot.blob --build-snapshot snapshot.js

    $ echo "console.log(globalThis.foo)" > index.js

    # Load the generated snapshot and start the application from index.js.
    $ node --snapshot-blob snapshot.blob index.js
    I am from the snapshot

The `v8.startupSnapshot` API can be used to specify an entry point at snapshot building time, thus avoiding the need of an additional entry script at deserialization time:

    $ echo "require('v8').startupSnapshot.setDeserializeMainFunction(() => console.log('I am from the snapshot'))" > snapshot.js
    $ node --snapshot-blob snapshot.blob --build-snapshot snapshot.js
    $ node --snapshot-blob snapshot.blob
    I am from the snapshot

For more information, check out the `v8.startupSnapshot` API documentation.

The snapshot currently only supports loding a single entrypoint during the snapshot building process, which can load built-in modules, but not additional user-land modules. Users can bundle their applications into a single script with their bundler of choice before building a snapshot.

As it's complicated to ensure the serializablility of all built-in modules, which are also growing over time, only a subset of the built-in modules are well tested to be serializable during the snapshot building process. The Node.js core test suite checks that a few fairly complex applications can be snapshotted. The list of built-in modules being captured by the built-in snapshot of Node.js is considered supported. When the snapshot builder encounters a built-in module that cannot be serialized, it may crash the snapshot building process. In that case a typical workaround would be to delay loading that module until runtime, using either `v8.startupSnapshot.setDeserializeMainFunction()` or `v8.startupSnapshot.addDeserializeCallback()`. If serialization for an additional module during the snapshot building process is needed, please file a request in the Node.js issue tracker and link to it in the tracking issue for user-land snapshots.

#### `--build-snapshot-config`#

History

Version | Changes
--- | ---
v24.13.1 | The snapshot building process is no longer experimental.
v21.6.0, v20.12.0 | Added in: v21.6.0, v20.12.0

Specifies the path to a JSON configuration file which configures snapshot creation behavior.

The following options are currently supported:

- `builder` <string> Required. Provides the name to the script that is executed before building the snapshot, as if `--build-snapshot` had been passed with `builder` as the main script name.
- `withoutCodeCache` <boolean> Optional. Including the code cache reduces the time spent on compiling functions included in the snapshot at the expense of a bigger snapshot size and potentially breaking portability of the snapshot.

When using this flag, additional script files provided on the command line will not be executed and instead be interpreted as regular command line arguments.

#### `-c`, `--check`#

History

Version | Changes
--- | ---
v10.0.0 | The `--require` option is now supported when checking a file.
v5.0.0, v4.2.0 | Added in: v5.0.0, v4.2.0

Syntax check the script without executing.

#### `--completion-bash`#

Added in: v10.12.0

Print source-able bash completion script for Node.js.

    node --completion-bash > node_bash_completion
    source node_bash_completion

#### `-C condition`, `--conditions=condition`#

History

Version | Changes
--- | ---
v22.9.0, v20.18.0 | The flag is no longer experimental.
v14.9.0, v12.19.0 | Added in: v14.9.0, v12.19.0

Provide custom conditional exports resolution conditions.

Any number of custom string condition names are permitted.

The default Node.js conditions of `"node"`, `"default"`, `"import"`, and `"require"` will always apply as defined.

For example, to run a module with "development" resolutions:

    node -C development app.js

#### `--cpu-prof`#

History

Version | Changes
--- | ---
v22.4.0, v20.16.0 | The `--cpu-prof` flags are now stable.
v12.0.0 | Added in: v12.0.0

Starts the V8 CPU profiler on start up, and writes the CPU profile to disk before exit.

If `--cpu-prof-dir` is not specified, the generated profile is placed in the current working directory.

If `--cpu-prof-name` is not specified, the generated profile is named `CPU.${yyyymmdd}.${hhmmss}.${pid}.${tid}.${seq}.cpuprofile`.

    $ node --cpu-prof index.js
    $ ls *.cpuprofile
    CPU.20190409.202950.15293.0.0.cpuprofile

If `--cpu-prof-name` is specified, the provided value is used as a template for the file name. The following placeholder is supported and will be substituted at runtime:

- `${pid}` — the current process ID

    $ node --cpu-prof --cpu-prof-name 'CPU.${pid}.cpuprofile' index.js
    $ ls *.cpuprofile
    CPU.15293.cpuprofile

#### `--cpu-prof-dir`#

History

Version | Changes
--- | ---
v22.4.0, v20.16.0 | The `--cpu-prof` flags are now stable.
v12.0.0 | Added in: v12.0.0

Specify the directory where the CPU profiles generated by `--cpu-prof` will be placed.

The default value is controlled by the `--diagnostic-dir` command-line option.

#### `--cpu-prof-interval`#

History

Version | Changes
--- | ---
v22.4.0, v20.16.0 | The `--cpu-prof` flags are now stable.
v12.2.0 | Added in: v12.2.0

Specify the sampling interval in microseconds for the CPU profiles generated by `--cpu-prof`. The default is 1000 microseconds.

#### `--cpu-prof-name`#

History

Version | Changes
--- | ---
v22.4.0, v20.16.0 | The `--cpu-prof` flags are now stable.
v12.0.0 | Added in: v12.0.0

Specify the file name of the CPU profile generated by `--cpu-prof`.

#### `--diagnostic-dir=directory`#

Set the directory to which all diagnostic output files are written. Defaults to current working directory.

Affects the default output directory of:

- `--cpu-prof-dir`
- `--heap-prof-dir`
- `--redirect-warnings`

#### `--disable-proto=mode`#

Added in: v13.12.0, v12.17.0

Disable the `Object.prototype.__proto__` property. If `mode` is `delete`, the property is removed entirely. If `mode` is `throw`, accesses to the property throw an exception with the code `ERR_PROTO_ACCESS`.

#### `--disable-sigusr1`#

History

Version | Changes
--- | ---
v24.8.0 | The option is no longer experimental.
v23.7.0, v22.14.0 | Added in: v23.7.0, v22.14.0

Disable the ability of starting a debugging session by sending a `SIGUSR1` signal to the process.

#### `--disable-warning=code-or-type`#

Added in: v21.3.0, v20.11.0

Stability: 1.1 - Active development

Disable specific process warnings by `code` or `type`.

Warnings emitted from `process.emitWarning()` may contain a `code` and a `type`. This option will not-emit warnings that have a matching `code` or `type`.

List of deprecation warnings.

The Node.js core warning types are: `DeprecationWarning` and `ExperimentalWarning`

For example, the following script will not emit DEP0025 `require('node:sys')` when executed with `node --disable-warning=DEP0025`:

    import sys from 'node:sys';const sys = require('node:sys');

For example, the following script will emit the DEP0025 `require('node:sys')`, but not any Experimental Warnings (such as ExperimentalWarning: `vm.measureMemory` is an experimental feature in <=v21) when executed with `node --disable-warning=ExperimentalWarning`:

    import sys from 'node:sys';
    import vm from 'node:vm';

    vm.measureMemory();const sys = require('node:sys');
    const vm = require('node:vm');

    vm.measureMemory();

#### `--disable-wasm-trap-handler`#

Added in: v22.2.0, v20.15.0

By default, Node.js enables trap-handler-based WebAssembly bound checks. As a result, V8 does not need to insert inline bound checks int the code compiled from WebAssembly which may speedup WebAssembly execution significantly, but this optimization requires allocating a big virtual memory cage (currently 10GB). If the Node.js process does not have access to a large enough virtual memory address space due to system configurations or hardware limitations, users won't be able to run any WebAssembly that involves allocation in this virtual memory cage and will see an out-of-memory error.

    $ ulimit -v 5000000
    $ node -p "new WebAssembly.Memory({ initial: 10, maximum: 100 });"
    [eval]:1
    new WebAssembly.Memory({ initial: 10, maximum: 100 });
    ^

    RangeError: WebAssembly.Memory(): could not allocate memory
        at [eval]:1:1
        at runScriptInThisContext (node:internal/vm:209:10)
        at node:internal/process/execution:118:14
        at [eval]-wrapper:6:24
        at runScript (node:internal/process/execution:101:62)
        at evalScript (node:internal/process/execution:136:3)
        at node:internal/main/eval_string:49:3

`--disable-wasm-trap-handler` disables this optimization so that users can at least run WebAssembly (with less optimal performance) when the virtual memory address space available to their Node.js process is lower than what the V8 WebAssembly memory cage needs.

#### `--disallow-code-generation-from-strings`#

Added in: v9.8.0

Make built-in language features like `eval` and `new Function` that generate code from strings throw an exception instead. This does not affect the Node.js `node:vm` module.

#### `--dns-result-order=order`#

History

Version | Changes
--- | ---
v22.1.0, v20.13.0 | The `ipv6first` is supported now.
v17.0.0 | Changed default value to `verbatim`.
v16.4.0, v14.18.0 | Added in: v16.4.0, v14.18.0

Set the default value of `order` in `dns.lookup()` and `dnsPromises.lookup()`. The value could be:

- `ipv4first`: sets default `order` to `ipv4first`.
- `ipv6first`: sets default `order` to `ipv6first`.
- `verbatim`: sets default `order` to `verbatim`.

The default is `verbatim` and `dns.setDefaultResultOrder()` have higher priority than `--dns-result-order`.

#### `--enable-fips`#

Added in: v6.0.0

Enable FIPS-compliant crypto at startup. (Requires Node.js to be built against FIPS-compatible OpenSSL.)

#### `--enable-network-family-autoselection`#

Added in: v18.18.0

Enables the family autoselection algorithm unless connection options explicitly disables it.

#### `--enable-source-maps`#

History

Version | Changes
--- | ---
v15.11.0, v14.18.0 | This API is no longer experimental.
v12.12.0 | Added in: v12.12.0

Enable Source Map support for stack traces.

When using a transpiler, such as TypeScript, stack traces thrown by an application reference the transpiled code, not the original source position. `--enable-source-maps` enables caching of Source Maps and makes a best effort to report stack traces relative to the original source file.

Overriding `Error.prepareStackTrace` may prevent `--enable-source-maps` from modifying the stack trace. Call and return the results of the original `Error.prepareStackTrace` in the overriding function to modify the stack trace with source maps.

    const originalPrepareStackTrace = Error.prepareStackTrace;
    Error.prepareStackTrace = (error, trace) => {
      // Modify error and trace and format stack trace with
      // original Error.prepareStackTrace.
      return originalPrepareStackTrace(error, trace);
    };

Note, enabling source maps can introduce latency to your application when `Error.stack` is accessed. If you access `Error.stack` frequently in your application, take into account the performance implications of `--enable-source-maps`.

#### `--entry-url`#

Added in: v23.0.0, v22.10.0

Stability: 1 - Experimental

When present, Node.js will interpret the entry point as a URL, rather than a path.

Follows ECMAScript module resolution rules.

Any query parameter or hash in the URL will be accessible via `import.meta.url`.

    node --entry-url 'file:///path/to/file.js?queryparams=work#and-hashes-too'
    node --entry-url 'file.ts?query#hash'
    node --entry-url 'data:text/javascript,console.log("Hello")'

#### `--env-file-if-exists=file`#

History

Version | Changes
--- | ---
v24.10.0 | The `--env-file-if-exists` flag is no longer experimental.
v22.9.0 | Added in: v22.9.0

Behavior is the same as `--env-file`, but an error is not thrown if the file does not exist.

#### `--env-file=file`#

History

Version | Changes
--- | ---
v24.10.0 | The `--env-file` flag is no longer experimental.
v21.7.0, v20.12.0 | Add support to multi-line values.
v20.6.0 | Added in: v20.6.0

Loads environment variables from a file relative to the current directory, making them available to applications on `process.env`. The environment variables which configure Node.js, such as `NODE_OPTIONS`, are parsed and applied. If the same variable is defined in the environment and in the file, the value from the environment takes precedence.

You can pass multiple `--env-file` arguments. Subsequent files override pre-existing variables defined in previous files.

An error is thrown if the file does not exist.

    node --env-file=.env --env-file=.development.env index.js

The format of the file should be one line per key-value pair of environment variable name and value separated by `=`:

    PORT=3000

Any text after a `#` is treated as a comment:

    # This is a comment
    PORT=3000 # This is also a comment

Values can start and end with the following quotes: ```, `"` or `'`. They are omitted from the values.

    USERNAME="nodejs" # will result in `nodejs` as the value.

Multi-line values are supported:

    MULTI_LINE="THIS IS
    A MULTILINE"
    # will result in `THIS IS\nA MULTILINE` as the value.

Export keyword before a key is ignored:

    export USERNAME="nodejs" # will result in `nodejs` as the value.

If you want to load environment variables from a file that may not exist, you can use the `--env-file-if-exists` flag instead.

#### `-e`, `--eval "script"`#

History

Version | Changes
--- | ---
v22.6.0 | Eval now supports experimental type-stripping.
v5.11.0 | Built-in libraries are now available as predefined variables.
v0.5.2 | Added in: v0.5.2

Evaluate the following argument as JavaScript. The modules which are predefined in the REPL can also be used in `script`.

On Windows, using `cmd.exe` a single quote will not work correctly because it only recognizes double `"` for quoting. In Powershell or Git bash, both `'` and `"` are usable.

It is possible to run code containing inline types unless the `--no-strip-types` flag is provided.

#### `--experimental-addon-modules`#

Added in: v23.6.0

Stability: 1.0 - Early development

Enable experimental import support for `.node` addons.

#### `--experimental-config-file=config`#

Added in: v23.10.0

Stability: 1.0 - Early development

If present, Node.js will look for a configuration file at the specified path. Node.js will read the configuration file and apply the settings. The configuration file should be a JSON file with the following structure. `vX.Y.Z` in the `$schema` must be replaced with the version of Node.js you are using.

    {
      "$schema": "https://nodejs.org/dist/vX.Y.Z/docs/node-config-schema.json",
      "nodeOptions": {
        "import": [
          "amaro/strip"
        ],
        "watch-path": "src",
        "watch-preserve-output": true
      },
      "testRunner": {
        "test-isolation": "process"
      },
      "watch": {
        "watch-preserve-output": true
      }
    }

The configuration file supports namespace-specific options:

- The `nodeOptions` field contains CLI flags that are allowed in `NODE_OPTIONS`.

- Namespace fields like `testRunner` contain configuration specific to that subsystem.

No-op flags are not supported. Not all V8 flags are currently supported.

It is possible to use the official JSON schema to validate the configuration file, which may vary depending on the Node.js version. Each key in the configuration file corresponds to a flag that can be passed as a command-line argument. The value of the key is the value that would be passed to the flag.

For example, the configuration file above is equivalent to the following command-line arguments:

    node --import amaro/strip --watch-path=src --watch-preserve-output --test-isolation=process

The priority in configuration is as follows:

1. NODE_OPTIONS and command-line options
2. Configuration file
3. Dotenv NODE_OPTIONS

Values in the configuration file will not override the values in the environment variables and command-line options, but will override the values in the `NODE_OPTIONS` env file parsed by the `--env-file` flag.

Keys cannot be duplicated within the same or different namespaces.

The configuration parser will throw an error if the configuration file contains unknown keys or keys that cannot be used in a namespace.

Node.js will not sanitize or perform validation on the user-provided configuration, so NEVER use untrusted configuration files.

#### `--experimental-default-config-file`#

Added in: v23.10.0

Stability: 1.0 - Early development

If the `--experimental-default-config-file` flag is present, Node.js will look for a `node.config.json` file in the current working directory and load it as a as configuration file.

#### `--experimental-eventsource`#

Added in: v22.3.0, v20.18.0

Enable exposition of EventSource Web API on the global scope.

#### `--experimental-import-meta-resolve`#

History

Version | Changes
--- | ---
v20.6.0, v18.19.0 | synchronous import.meta.resolve made available by default, with the flag retained for enabling the experimental second argument as previously supported.
v13.9.0, v12.16.2 | Added in: v13.9.0, v12.16.2

Enable experimental `import.meta.resolve()` parent URL support, which allows passing a second `parentURL` argument for contextual resolution.

Previously gated the entire `import.meta.resolve` feature.

#### `--experimental-inspector-network-resource`#

Added in: v24.5.0

Stability: 1.1 - Active Development

Enable experimental support for inspector network resources.

#### `--experimental-loader=module`#

History

Version | Changes
--- | ---
v23.6.1, v22.13.1, v20.18.2 | Using this feature with the permission model enabled requires passing `--allow-worker`.
v12.11.1 | This flag was renamed from `--loader` to `--experimental-loader`.
v8.8.0 | Added in: v8.8.0

> This flag is discouraged and may be removed in a future version of Node.js. Please use `--import` with `register()` instead.

Specify the `module` containing exported asynchronous module customization hooks. `module` may be any string accepted as an `import` specifier.

This feature requires `--allow-worker` if used with the Permission Model.

#### `--experimental-network-inspection`#

Added in: v22.6.0, v20.18.0

Stability: 1 - Experimental

Enable experimental support for the network inspection with Chrome DevTools.

#### `--experimental-print-required-tla`#

Added in: v22.0.0, v20.17.0

If the ES module being `require()`'d contains top-level `await`, this flag allows Node.js to evaluate the module, try to locate the top-level awaits, and print their location to help users find them.

#### `--experimental-require-module`#

History

Version | Changes
--- | ---
v23.0.0, v22.12.0, v20.19.0 | This is now true by default.
v22.0.0, v20.17.0 | Added in: v22.0.0, v20.17.0

Stability: 1.1 - Active Development

Supports loading a synchronous ES module graph in `require()`.

See Loading ECMAScript modules using `require()`.

#### `--experimental-sea-config`#

Added in: v20.0.0

Stability: 1 - Experimental

Use this flag to generate a blob that can be injected into the Node.js binary to produce a single executable application. See the documentation about this configuration for details.

#### `--experimental-shadow-realm`#

Added in: v19.0.0, v18.13.0

Use this flag to enable ShadowRealm support.

#### `--experimental-test-coverage`#

History

Version | Changes
--- | ---
v20.1.0, v18.17.0 | This option can be used with `--test`.
v19.7.0, v18.15.0 | Added in: v19.7.0, v18.15.0

When used in conjunction with the `node:test` module, a code coverage report is generated as part of the test runner output. If no tests are run, a coverage report is not generated. See the documentation on collecting code coverage from tests for more details.

#### `--experimental-test-module-mocks`#

History

Version | Changes
--- | ---
v23.6.1, v22.13.1, v20.18.2 | Using this feature with the permission model enabled requires passing `--allow-worker`.
v22.3.0, v20.18.0 | Added in: v22.3.0, v20.18.0

Stability: 1.0 - Early development

Enable module mocking in the test runner.

This feature requires `--allow-worker` if used with the Permission Model.

#### `--experimental-transform-types`#

Added in: v22.7.0

Stability: 1.2 - Release candidate

Enables the transformation of TypeScript-only syntax into JavaScript code. Implies `--enable-source-maps`.

#### `--experimental-vm-modules`#

Added in: v9.6.0

Enable experimental ES Module support in the `node:vm` module.

#### `--experimental-wasi-unstable-preview1`#

History

Version | Changes
--- | ---
v20.0.0, v18.17.0 | This option is no longer required as WASI is enabled by default, but can still be passed.
v13.6.0 | changed from `--experimental-wasi-unstable-preview0` to `--experimental-wasi-unstable-preview1`.
v13.3.0, v12.16.0 | Added in: v13.3.0, v12.16.0

Enable experimental WebAssembly System Interface (WASI) support.

#### `--experimental-webstorage`#

Added in: v22.4.0

Stability: 1.2 - Release candidate.

Enable `Web Storage` support.

#### `--experimental-worker-inspection`#

Added in: v24.1.0

Stability: 1.1 - Active Development

Enable experimental support for the worker inspection with Chrome DevTools.

#### `--expose-gc`#

Added in: v22.3.0, v20.18.0

Stability: 1 - Experimental. This flag is inherited from V8 and is subject to change upstream.

This flag will expose the gc extension from V8.

    if (globalThis.gc) {
      globalThis.gc();
    }

#### `--force-context-aware`#

Added in: v12.12.0

Disable loading native addons that are not context-aware.

#### `--force-fips`#

Added in: v6.0.0

Force FIPS-compliant crypto on startup. (Cannot be disabled from script code.) (Same requirements as `--enable-fips`.)

#### `--force-node-api-uncaught-exceptions-policy`#

Added in: v18.3.0, v16.17.0

Enforces `uncaughtException` event on Node-API asynchronous callbacks.

To prevent from an existing add-on from crashing the process, this flag is not enabled by default. In the future, this flag will be enabled by default to enforce the correct behavior.

#### `--frozen-intrinsics`#

Added in: v11.12.0

Stability: 1 - Experimental

Enable experimental frozen intrinsics like `Array` and `Object`.

Only the root context is supported. There is no guarantee that `globalThis.Array` is indeed the default intrinsic reference. Code may break under this flag.

To allow polyfills to be added, `--require` and `--import` both run before freezing intrinsics.

#### `--heap-prof`#

History

Version | Changes
--- | ---
v22.4.0, v20.16.0 | The `--heap-prof` flags are now stable.
v12.4.0 | Added in: v12.4.0

Starts the V8 heap profiler on start up, and writes the heap profile to disk before exit.

If `--heap-prof-dir` is not specified, the generated profile is placed in the current working directory.

If `--heap-prof-name` is not specified, the generated profile is named `Heap.${yyyymmdd}.${hhmmss}.${pid}.${tid}.${seq}.heapprofile`.

    $ node --heap-prof index.js
    $ ls *.heapprofile
    Heap.20190409.202950.15293.0.001.heapprofile

#### `--heap-prof-dir`#

History

Version | Changes
--- | ---
v22.4.0, v20.16.0 | The `--heap-prof` flags are now stable.
v12.4.0 | Added in: v12.4.0

Specify the directory where the heap profiles generated by `--heap-prof` will be placed.

The default value is controlled by the `--diagnostic-dir` command-line option.

#### `--heap-prof-interval`#

History

Version | Changes
--- | ---
v22.4.0, v20.16.0 | The `--heap-prof` flags are now stable.
v12.4.0 | Added in: v12.4.0

Specify the average sampling interval in bytes for the heap profiles generated by `--heap-prof`. The default is 512 * 1024 bytes.

#### `--heap-prof-name`#

History

Version | Changes
--- | ---
v22.4.0, v20.16.0 | The `--heap-prof` flags are now stable.
v12.4.0 | Added in: v12.4.0

Specify the file name of the heap profile generated by `--heap-prof`.

#### `--heapsnapshot-near-heap-limit=max_count`#

History

Version | Changes
--- | ---
v24.13.1 | The flag is no longer experimental.
v15.1.0, v14.18.0 | Added in: v15.1.0, v14.18.0

Writes a V8 heap snapshot to disk when the V8 heap usage is approaching the heap limit. `count` should be a non-negative integer (in which case Node.js will write no more than `max_count` snapshots to disk).

When generating snapshots, garbage collection may be triggered and bring the heap usage down. Therefore multiple snapshots may be written to disk before the Node.js instance finally runs out of memory. These heap snapshots can be compared to determine what objects are being allocated during the time consecutive snapshots are taken. It's not guaranteed that Node.js will write exactly `max_count` snapshots to disk, but it will try its best to generate at least one and up to `max_count` snapshots before the Node.js instance runs out of memory when `max_count` is greater than `0`.

Generating V8 snapshots takes time and memory (both memory managed by the V8 heap and native memory outside the V8 heap). The bigger the heap is, the more resources it needs. Node.js will adjust the V8 heap to accommodate the additional V8 heap memory overhead, and try its best to avoid using up all the memory available to the process. When the process uses more memory than the system deems appropriate, the process may be terminated abruptly by the system, depending on the system configuration.

    $ node --max-old-space-size=100 --heapsnapshot-near-heap-limit=3 index.js
    Wrote snapshot to Heap.20200430.100036.49580.0.001.heapsnapshot
    Wrote snapshot to Heap.20200430.100037.49580.0.002.heapsnapshot
    Wrote snapshot to Heap.20200430.100038.49580.0.003.heapsnapshot

    <--- Last few GCs --->

    [49580:0x110000000]     4826 ms: Mark-sweep 130.6 (147.8) -> 130.5 (147.8) MB, 27.4 / 0.0 ms  (average mu = 0.126, current mu = 0.034) allocation failure scavenge might not succeed
    [49580:0x110000000]     4845 ms: Mark-sweep 130.6 (147.8) -> 130.6 (147.8) MB, 18.8 / 0.0 ms  (average mu = 0.088, current mu = 0.031) allocation failure scavenge might not succeed

    <--- JS stacktrace --->

    FATAL ERROR: Ineffective mark-compacts near heap limit Allocation failed - JavaScript heap out of memory
    ....

#### `--heapsnapshot-signal=signal`#

Added in: v12.0.0

Enables a signal handler that causes the Node.js process to write a heap dump when the specified signal is received. `signal` must be a valid signal name. Disabled by default.

    $ node --heapsnapshot-signal=SIGUSR2 index.js &
    $ ps aux
    USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
    node         1  5.5  6.1 787252 247004 ?       Ssl  16:43   0:02 node --heapsnapshot-signal=SIGUSR2 index.js
    $ kill -USR2 1
    $ ls
    Heap.20190718.133405.15554.0.001.heapsnapshot

#### `-h`, `--help`#

Added in: v0.1.3

Print node command-line options. The output of this option is less detailed than this document.

#### `--icu-data-dir=file`#

Added in: v0.11.15

Specify ICU data load path. (Overrides `NODE_ICU_DATA`.)

#### `--import=module`#

Added in: v19.0.0, v18.18.0

Stability: 1 - Experimental

Preload the specified module at startup. If the flag is provided several times, each module will be executed sequentially in the order they appear, starting with the ones provided in `NODE_OPTIONS`.

Follows ECMAScript module resolution rules. Use `--require` to load a CommonJS module. Modules preloaded with `--require` will run before modules preloaded with `--import`.

Modules are preloaded into the main thread as well as any worker threads, forked processes, or clustered processes.

#### `--input-type=type`#

History

Version | Changes
--- | ---
v23.6.0 | Add support for `-typescript` values.
v22.7.0, v20.19.0 | ESM syntax detection is enabled by default.
v12.0.0 | Added in: v12.0.0

This configures Node.js to interpret `--eval` or `STDIN` input as CommonJS or as an ES module. Valid values are `"commonjs"`, `"module"`, `"module-typescript"` and `"commonjs-typescript"`. The `"-typescript"` values are not available with the flag `--no-strip-types`. The default is no value, or `"commonjs"` if `--no-experimental-detect-module` is passed.

If `--input-type` is not provided, Node.js will try to detect the syntax with the following steps:

1. Run the input as CommonJS.
2. If step 1 fails, run the input as an ES module.
3. If step 2 fails with a SyntaxError, strip the types.
4. If step 3 fails with an error code `ERR_UNSUPPORTED_TYPESCRIPT_SYNTAX` or `ERR_INVALID_TYPESCRIPT_SYNTAX`, throw the error from step 2, including the TypeScript error in the message, else run as CommonJS.
5. If step 4 fails, run the input as an ES module.

To avoid the delay of multiple syntax detection passes, the `--input-type=type` flag can be used to specify how the `--eval` input should be interpreted.

The REPL does not support this option. Usage of `--input-type=module` with `--print` will throw an error, as `--print` does not support ES module syntax.

#### `--insecure-http-parser`#

Added in: v13.4.0, v12.15.0, v10.19.0

Enable leniency flags on the HTTP parser. This may allow interoperability with non-conformant HTTP implementations.

When enabled, the parser will accept the following:

- Invalid HTTP headers values.
- Invalid HTTP versions.
- Allow message containing both `Transfer-Encoding` and `Content-Length` headers.
- Allow extra data after message when `Connection: close` is present.
- Allow extra transfer encodings after `chunked` has been provided.
- Allow `\n` to be used as token separator instead of `\r\n`.
- Allow `\r\n` not to be provided after a chunk.
- Allow spaces to be present after a chunk size and before `\r\n`.

All the above will expose your application to request smuggling or poisoning attack. Avoid using this option.

#### `--inspect-brk[=[host:]port]`#

Added in: v7.6.0

Activate inspector on `host:port` and break at start of user script. Default `host:port` is `127.0.0.1:9229`. If port `0` is specified, a random available port will be used.

See V8 Inspector integration for Node.js for further explanation on Node.js debugger.

See the security warning below regarding the `host` parameter usage.

#### `--inspect-port=[host:]port`#

Added in: v7.6.0

Set the `host:port` to be used when the inspector is activated. Useful when activating the inspector by sending the `SIGUSR1` signal. Except when `--disable-sigusr1` is passed.

Default host is `127.0.0.1`. If port `0` is specified, a random available port will be used.

See the security warning below regarding the `host` parameter usage.

#### `--inspect-publish-uid=stderr,http`#

Specify ways of the inspector web socket url exposure.

By default inspector websocket url is available in stderr and under `/json/list` endpoint on `http://host:port/json/list`.

#### `--inspect-wait[=[host:]port]`#

Added in: v22.2.0, v20.15.0

Activate inspector on `host:port` and wait for debugger to be attached. Default `host:port` is `127.0.0.1:9229`. If port `0` is specified, a random available port will be used.

See V8 Inspector integration for Node.js for further explanation on Node.js debugger.

See the security warning below regarding the `host` parameter usage.

#### `--inspect[=[host:]port]`#

Added in: v6.3.0

Activate inspector on `host:port`. Default is `127.0.0.1:9229`. If port `0` is specified, a random available port will be used.

V8 inspector integration allows tools such as Chrome DevTools and IDEs to debug and profile Node.js instances. The tools attach to Node.js instances via a tcp port and communicate using the Chrome DevTools Protocol. See V8 Inspector integration for Node.js for further explanation on Node.js debugger.

##### Warning: binding inspector to a public IP:port combination is insecure#

Binding the inspector to a public IP (including `0.0.0.0`) with an open port is insecure, as it allows external hosts to connect to the inspector and perform a remote code execution attack.

If specifying a host, make sure that either:

- The host is not accessible from public networks.
- A firewall disallows unwanted connections on the port.

More specifically, `--inspect=0.0.0.0` is insecure if the port (`9229` by default) is not firewall-protected.

See the debugging security implications section for more information.

#### `-i`, `--interactive`#

Added in: v0.7.7

Opens the REPL even if stdin does not appear to be a terminal.

#### `--jitless`#

Added in: v12.0.0

Stability: 1 - Experimental. This flag is inherited from V8 and is subject to change upstream.

Disable runtime allocation of executable memory. This may be required on some platforms for security reasons. It can also reduce attack surface on other platforms, but the performance impact may be severe.

#### `--localstorage-file=file`#

Added in: v22.4.0

Stability: 1.2 - Release candidate. Enable this API with `--experimental-webstorage`.

The file used to store `localStorage` data. If the file does not exist, it is created the first time `localStorage` is accessed. The same file may be shared between multiple Node.js processes concurrently.

#### `--max-http-header-size=size`#

History

Version | Changes
--- | ---
v13.13.0 | Change maximum default size of HTTP headers from 8 KiB to 16 KiB.
v11.6.0, v10.15.0 | Added in: v11.6.0, v10.15.0

Specify the maximum size, in bytes, of HTTP headers. Defaults to 16 KiB.

#### `--max-old-space-size-percentage=percentage`#

Sets the maximum memory size of V8's old memory section as a percentage of available system memory. This flag takes precedence over `--max-old-space-size` when both are specified.

The `percentage` parameter must be a number greater than 0 and up to 100, representing the percentage of available system memory to allocate to the V8 heap.

Note: This flag utilizes `--max-old-space-size`, which may be unreliable on 32-bit platforms due to integer overflow issues.

    # Using 50% of available system memory
    node --max-old-space-size-percentage=50 index.js

    # Using 75% of available system memory
    node --max-old-space-size-percentage=75 index.js

#### `--napi-modules`#

Added in: v7.10.0

This option is a no-op. It is kept for compatibility.

#### `--network-family-autoselection-attempt-timeout`#

Added in: v22.1.0, v20.13.0

Sets the default value for the network family autoselection attempt timeout. For more information, see `net.getDefaultAutoSelectFamilyAttemptTimeout()`.

#### `--no-addons`#

Added in: v16.10.0, v14.19.0

Disable the `node-addons` exports condition as well as disable loading native addons. When `--no-addons` is specified, calling `process.dlopen` or requiring a native C++ addon will fail and throw an exception.

#### `--no-async-context-frame`#

Added in: v24.0.0

Disables the use of `AsyncLocalStorage` backed by `AsyncContextFrame` and uses the prior implementation which relied on async_hooks. The previous model is retained for compatibility with Electron and for cases where the context flow may differ. However, if a difference in flow is found please report it.

#### `--no-deprecation`#

Added in: v0.8.0

Silence deprecation warnings.

#### `--no-experimental-detect-module`#

History

Version | Changes
--- | ---
v22.7.0, v20.19.0 | Syntax detection is enabled by default.
v21.1.0, v20.10.0 | Added in: v21.1.0, v20.10.0

Disable using syntax detection to determine module type.

#### `--no-experimental-global-navigator`#

Added in: v21.2.0

Stability: 1 - Experimental

Disable exposition of Navigator API on the global scope.

#### `--no-experimental-repl-await`#

Added in: v16.6.0

Use this flag to disable top-level await in REPL.

#### `--no-experimental-require-module`#

History

Version | Changes
--- | ---
v23.0.0, v22.12.0, v20.19.0 | This is now false by default.
v22.0.0, v20.17.0 | Added in: v22.0.0, v20.17.0

Stability: 1.1 - Active Development

Disable support for loading a synchronous ES module graph in `require()`.

See Loading ECMAScript modules using `require()`.

#### `--no-experimental-sqlite`#

History

Version | Changes
--- | ---
v23.4.0, v22.13.0 | SQLite is unflagged but still experimental.
v22.5.0 | Added in: v22.5.0

Disable the experimental `node:sqlite` module.

#### `--no-experimental-websocket`#

Added in: v22.0.0

Disable exposition of <WebSocket> on the global scope.

#### `--no-extra-info-on-fatal-exception`#

Added in: v17.0.0

Hide extra information on fatal exception that causes exit.

#### `--no-force-async-hooks-checks`#

Added in: v9.0.0

Disables runtime checks for `async_hooks`. These will still be enabled dynamically when `async_hooks` is enabled.

#### `--no-global-search-paths`#

Added in: v16.10.0

Do not search modules from global paths like `$HOME/.node_modules` and `$NODE_PATH`.

#### `--no-network-family-autoselection`#

History

Version | Changes
--- | ---
v20.0.0 | The flag was renamed from `--no-enable-network-family-autoselection` to `--no-network-family-autoselection`. The old name can still work as an alias.
v19.4.0 | Added in: v19.4.0

Disables the family autoselection algorithm unless connection options explicitly enables it.

#### `--no-strip-types`#

History

Version | Changes
--- | ---
v24.12.0 | Type stripping is now stable, the flag was renamed from `--no-experimental-strip-types` to `--no-strip-types`.
v23.6.0, v22.18.0 | Type stripping is enabled by default.
v22.6.0 | Added in: v22.6.0

Disable type-stripping for TypeScript files. For more information, see the TypeScript type-stripping documentation.

#### `--no-warnings`#

Added in: v6.0.0

Silence all process warnings (including deprecations).

#### `--node-memory-debug`#

Added in: v15.0.0, v14.18.0

Enable extra debug checks for memory leaks in Node.js internals. This is usually only useful for developers debugging Node.js itself.

#### `--openssl-config=file`#

Added in: v6.9.0

Load an OpenSSL configuration file on startup. Among other uses, this can be used to enable FIPS-compliant crypto if Node.js is built against FIPS-enabled OpenSSL.

#### `--openssl-legacy-provider`#

Added in: v17.0.0, v16.17.0

Enable OpenSSL 3.0 legacy provider. For more information please see OSSL_PROVIDER-legacy.

#### `--openssl-shared-config`#

Added in: v18.5.0, v16.17.0, v14.21.0

Enable OpenSSL default configuration section, `openssl_conf` to be read from the OpenSSL configuration file. The default configuration file is named `openssl.cnf` but this can be changed using the environment variable `OPENSSL_CONF`, or by using the command line option `--openssl-config`. The location of the default OpenSSL configuration file depends on how OpenSSL is being linked to Node.js. Sharing the OpenSSL configuration may have unwanted implications and it is recommended to use a configuration section specific to Node.js which is `nodejs_conf` and is default when this option is not used.

#### `--pending-deprecation`#

Added in: v8.0.0

Emit pending deprecation warnings.

Pending deprecations are generally identical to a runtime deprecation with the notable exception that they are turned off by default and will not be emitted unless either the `--pending-deprecation` command-line flag, or the `NODE_PENDING_DEPRECATION=1` environment variable, is set. Pending deprecations are used to provide a kind of selective "early warning" mechanism that developers may leverage to detect deprecated API usage.

#### `--permission`#

History

Version | Changes
--- | ---
v23.5.0, v22.13.0 | Permission Model is now stable.
v20.0.0 | Added in: v20.0.0

Enable the Permission Model for current process. When enabled, the following permissions are restricted:

- File System - manageable through `--allow-fs-read`, `--allow-fs-write` flags
- Child Process - manageable through `--allow-child-process` flag
- Worker Threads - manageable through `--allow-worker` flag
- WASI - manageable through `--allow-wasi` flag
- Addons - manageable through `--allow-addons` flag

#### `--preserve-symlinks`#

Added in: v6.3.0

Instructs the module loader to preserve symbolic links when resolving and caching modules.

By default, when Node.js loads a module from a path that is symbolically linked to a different on-disk location, Node.js will dereference the link and use the actual on-disk "real path" of the module as both an identifier and as a root path to locate other dependency modules. In most cases, this default behavior is acceptable. However, when using symbolically linked peer dependencies, as illustrated in the example below, the default behavior causes an exception to be thrown if `moduleA` attempts to require `moduleB` as a peer dependency:

    {appDir}
     ├── app
     │   ├── index.js
     │   └── node_modules
     │       ├── moduleA -> {appDir}/moduleA
     │       └── moduleB
     │           ├── index.js
     │           └── package.json
     └── moduleA
         ├── index.js
         └── package.json

The `--preserve-symlinks` command-line flag instructs Node.js to use the symlink path for modules as opposed to the real path, allowing symbolically linked peer dependencies to be found.

Note, however, that using `--preserve-symlinks` can have other side effects. Specifically, symbolically linked native modules can fail to load if those are linked from more than one location in the dependency tree (Node.js would see those as two separate modules and would attempt to load the module multiple times, causing an exception to be thrown).

The `--preserve-symlinks` flag does not apply to the main module, which allows `node --preserve-symlinks node_module/.bin/<foo>` to work. To apply the same behavior for the main module, also use `--preserve-symlinks-main`.

#### `--preserve-symlinks-main`#

Added in: v10.2.0

Instructs the module loader to preserve symbolic links when resolving and caching the main module (`require.main`).

This flag exists so that the main module can be opted-in to the same behavior that `--preserve-symlinks` gives to all other imports; they are separate flags, however, for backward compatibility with older Node.js versions.

`--preserve-symlinks-main` does not imply `--preserve-symlinks`; use `--preserve-symlinks-main` in addition to `--preserve-symlinks` when it is not desirable to follow symlinks before resolving relative paths.

See `--preserve-symlinks` for more information.

#### `-p`, `--print "script"`#

History

Version | Changes
--- | ---
v5.11.0 | Built-in libraries are now available as predefined variables.
v0.6.4 | Added in: v0.6.4

Identical to `-e` but prints the result.

#### `--prof`#

Added in: v2.0.0

Generate V8 profiler output.

#### `--prof-process`#

Added in: v5.2.0

Process V8 profiler output generated using the V8 option `--prof`.

#### `--redirect-warnings=file`#

Added in: v8.0.0

Write process warnings to the given file instead of printing to stderr. The file will be created if it does not exist, and will be appended to if it does. If an error occurs while attempting to write the warning to the file, the warning will be written to stderr instead.

The `file` name may be an absolute path. If it is not, the default directory it will be written to is controlled by the `--diagnostic-dir` command-line option.

#### `--report-compact`#

Added in: v13.12.0, v12.17.0

Write reports in a compact format, single-line JSON, more easily consumable by log processing systems than the default multi-line format designed for human consumption.

#### `--report-dir=directory`, `report-directory=directory`#

History

Version | Changes
--- | ---
v13.12.0, v12.17.0 | This option is no longer experimental.
v12.0.0 | Changed from `--diagnostic-report-directory` to `--report-directory`.
v11.8.0 | Added in: v11.8.0

Location at which the report will be generated.

#### `--report-exclude-env`#

Added in: v23.3.0, v22.13.0

When `--report-exclude-env` is passed the diagnostic report generated will not contain the `environmentVariables` data.

#### `--report-exclude-network`#

Added in: v22.0.0, v20.13.0

Exclude `header.networkInterfaces` from the diagnostic report. By default this is not set and the network interfaces are included.

#### `--report-filename=filename`#

History

Version | Changes
--- | ---
v13.12.0, v12.17.0 | This option is no longer experimental.
v12.0.0 | changed from `--diagnostic-report-filename` to `--report-filename`.
v11.8.0 | Added in: v11.8.0

Name of the file to which the report will be written.

If the filename is set to `'stdout'` or `'stderr'`, the report is written to the stdout or stderr of the process respectively.

#### `--report-on-fatalerror`#

History

Version | Changes
--- | ---
v14.0.0, v13.14.0, v12.17.0 | This option is no longer experimental.
v12.0.0 | changed from `--diagnostic-report-on-fatalerror` to `--report-on-fatalerror`.
v11.8.0 | Added in: v11.8.0

Enables the report to be triggered on fatal errors (internal errors within the Node.js runtime such as out of memory) that lead to termination of the application. Useful to inspect various diagnostic data elements such as heap, stack, event loop state, resource consumption etc. to reason about the fatal error.

#### `--report-on-signal`#

History

Version | Changes
--- | ---
v13.12.0, v12.17.0 | This option is no longer experimental.
v12.0.0 | changed from `--diagnostic-report-on-signal` to `--report-on-signal`.
v11.8.0 | Added in: v11.8.0

Enables report to be generated upon receiving the specified (or predefined) signal to the running Node.js process. The signal to trigger the report is specified through `--report-signal`.

#### `--report-signal=signal`#

History

Version | Changes
--- | ---
v13.12.0, v12.17.0 | This option is no longer experimental.
v12.0.0 | changed from `--diagnostic-report-signal` to `--report-signal`.
v11.8.0 | Added in: v11.8.0

Sets or resets the signal for report generation (not supported on Windows). Default signal is `SIGUSR2`.

#### `--report-uncaught-exception`#

History

Version | Changes
--- | ---
v18.8.0, v16.18.0 | Report is not generated if the uncaught exception is handled.
v13.12.0, v12.17.0 | This option is no longer experimental.
v12.0.0 | changed from `--diagnostic-report-uncaught-exception` to `--report-uncaught-exception`.
v11.8.0 | Added in: v11.8.0

Enables report to be generated when the process exits due to an uncaught exception. Useful when inspecting the JavaScript stack in conjunction with native stack and other runtime environment data.

#### `-r`, `--require module`#

History

Version | Changes
--- | ---
v23.0.0, v22.12.0, v20.19.0 | This option also supports ECMAScript module.
v1.6.0 | Added in: v1.6.0

Preload the specified module at startup.

Follows `require()`'s module resolution rules. `module` may be either a path to a file, or a node module name.

Modules preloaded with `--require` will run before modules preloaded with `--import`.

Modules are preloaded into the main thread as well as any worker threads, forked processes, or clustered processes.

#### `--run`#

History

Version | Changes
--- | ---
v22.3.0 | NODE_RUN_SCRIPT_NAME environment variable is added.
v22.3.0 | NODE_RUN_PACKAGE_JSON_PATH environment variable is added.
v22.3.0 | Traverses up to the root directory and finds a `package.json` file to run the command from, and updates `PATH` environment variable accordingly.
v22.0.0 | Added in: v22.0.0

This runs a specified command from a package.json's `"scripts"` object. If a missing `"command"` is provided, it will list the available scripts.

`--run` will traverse up to the root directory and finds a `package.json` file to run the command from.

`--run` prepends `./node_modules/.bin` for each ancestor of the current directory, to the `PATH` in order to execute the binaries from different folders where multiple `node_modules` directories are present, if `ancestor-folder/node_modules/.bin` is a directory.

`--run` executes the command in the directory containing the related `package.json`.

For example, the following command will run the `test` script of the `package.json` in the current folder:

    $ node --run test

You can also pass arguments to the command. Any argument after `--` will be appended to the script:

    $ node --run test -- --verbose

##### Intentional limitations#

`node --run` is not meant to match the behaviors of `npm run` or of the `run` commands of other package managers. The Node.js implementation is intentionally more limited, in order to focus on top performance for the most common use cases. Some features of other `run` implementations that are intentionally excluded are:

- Running `pre` or `post` scripts in addition to the specified script.
- Defining package manager-specific environment variables.

##### Environment variables#

The following environment variables are set when running a script with `--run`:

- `NODE_RUN_SCRIPT_NAME`: The name of the script being run. For example, if `--run` is used to run `test`, the value of this variable will be `test`.
- `NODE_RUN_PACKAGE_JSON_PATH`: The path to the `package.json` that is being processed.

#### `--secure-heap-min=n`#

Added in: v15.6.0

When using `--secure-heap`, the `--secure-heap-min` flag specifies the minimum allocation from the secure heap. The minimum value is `2`. The maximum value is the lesser of `--secure-heap` or `2147483647`. The value given must be a power of two.

#### `--secure-heap=n`#

Added in: v15.6.0

Initializes an OpenSSL secure heap of `n` bytes. When initialized, the secure heap is used for selected types of allocations within OpenSSL during key generation and other operations. This is useful, for instance, to prevent sensitive information from leaking due to pointer overruns or underruns.

The secure heap is a fixed size and cannot be resized at runtime so, if used, it is important to select a large enough heap to cover all application uses.

The heap size given must be a power of two. Any value less than 2 will disable the secure heap.

The secure heap is disabled by default.

The secure heap is not available on Windows.

See `CRYPTO_secure_malloc_init` for more details.

#### `--snapshot-blob=path`#

Added in: v18.8.0

Stability: 1 - Experimental

When used with `--build-snapshot`, `--snapshot-blob` specifies the path where the generated snapshot blob is written to. If not specified, the generated blob is written to `snapshot.blob` in the current working directory.

When used without `--build-snapshot`, `--snapshot-blob` specifies the path to the blob that is used to restore the application state.

When loading a snapshot, Node.js checks that:

1. The version, architecture, and platform of the running Node.js binary are exactly the same as that of the binary that generates the snapshot.
2. The V8 flags and CPU features are compatible with that of the binary that generates the snapshot.

If they don't match, Node.js refuses to load the snapshot and exits with status code 1.

#### `--test`#

History

Version | Changes
--- | ---
v20.0.0 | The test runner is now stable.
v19.2.0, v18.13.0 | Test runner now supports running in watch mode.
v18.1.0, v16.17.0 | Added in: v18.1.0, v16.17.0

Starts the Node.js command line test runner. This flag cannot be combined with `--watch-path`, `--check`, `--eval`, `--interactive`, or the inspector. See the documentation on running tests from the command line for more details.

#### `--test-concurrency`#

Added in: v21.0.0, v20.10.0, v18.19.0

The maximum number of test files that the test runner CLI will execute concurrently. If `--test-isolation` is set to `'none'`, this flag is ignored and concurrency is one. Otherwise, concurrency defaults to `os.availableParallelism() - 1`.

#### `--test-coverage-branches=threshold`#

Added in: v22.8.0

Stability: 1 - Experimental

Require a minimum percent of covered branches. If code coverage does not reach the threshold specified, the process will exit with code `1`.

#### `--test-coverage-exclude`#

Added in: v22.5.0

Stability: 1 - Experimental

Excludes specific files from code coverage using a glob pattern, which can match both absolute and relative file paths.

This option may be specified multiple times to exclude multiple glob patterns.

If both `--test-coverage-exclude` and `--test-coverage-include` are provided, files must meet both criteria to be included in the coverage report.

By default all the matching test files are excluded from the coverage report. Specifying this option will override the default behavior.

#### `--test-coverage-functions=threshold`#

Added in: v22.8.0

Stability: 1 - Experimental

Require a minimum percent of covered functions. If code coverage does not reach the threshold specified, the process will exit with code `1`.

#### `--test-coverage-include`#

Added in: v22.5.0

Stability: 1 - Experimental

Includes specific files in code coverage using a glob pattern, which can match both absolute and relative file paths.

This option may be specified multiple times to include multiple glob patterns.

If both `--test-coverage-exclude` and `--test-coverage-include` are provided, files must meet both criteria to be included in the coverage report.

#### `--test-coverage-lines=threshold`#

Added in: v22.8.0

Stability: 1 - Experimental

Require a minimum percent of covered lines. If code coverage does not reach the threshold specified, the process will exit with code `1`.

#### `--test-force-exit`#

Added in: v22.0.0, v20.14.0

Configures the test runner to exit the process once all known tests have finished executing even if the event loop would otherwise remain active.

#### `--test-global-setup=module`#

Added in: v24.0.0

Stability: 1.0 - Early development

Specify a module that will be evaluated before all tests are executed and can be used to setup global state or fixtures for tests.

See the documentation on global setup and teardown for more details.

#### `--test-isolation=mode`#

History

Version | Changes
--- | ---
v23.6.0 | This flag was renamed from `--experimental-test-isolation` to `--test-isolation`.
v22.8.0 | Added in: v22.8.0

Configures the type of test isolation used in the test runner. When `mode` is `'process'`, each test file is run in a separate child process. When `mode` is `'none'`, all test files run in the same process as the test runner. The default isolation mode is `'process'`. This flag is ignored if the `--test` flag is not present. See the test runner execution model section for more information.

#### `--test-name-pattern`#

History

Version | Changes
--- | ---
v20.0.0 | The test runner is now stable.
v18.11.0 | Added in: v18.11.0

A regular expression that configures the test runner to only execute tests whose name matches the provided pattern. See the documentation on filtering tests by name for more details.

If both `--test-name-pattern` and `--test-skip-pattern` are supplied, tests must satisfy both requirements in order to be executed.

#### `--test-only`#

History

Version | Changes
--- | ---
v20.0.0 | The test runner is now stable.
v18.0.0, v16.17.0 | Added in: v18.0.0, v16.17.0

Configures the test runner to only execute top level tests that have the `only` option set. This flag is not necessary when test isolation is disabled.

#### `--test-reporter`#

History

Version | Changes
--- | ---
v20.0.0 | The test runner is now stable.
v19.6.0, v18.15.0 | Added in: v19.6.0, v18.15.0

A test reporter to use when running tests. See the documentation on test reporters for more details.

#### `--test-reporter-destination`#

History

Version | Changes
--- | ---
v20.0.0 | The test runner is now stable.
v19.6.0, v18.15.0 | Added in: v19.6.0, v18.15.0

The destination for the corresponding test reporter. See the documentation on test reporters for more details.

#### `--test-rerun-failures`#

Added in: v24.7.0

A path to a file allowing the test runner to persist the state of the test suite between runs. The test runner will use this file to determine which tests have already succeeded or failed, allowing for re-running of failed tests without having to re-run the entire test suite. The test runner will create this file if it does not exist. See the documentation on test reruns for more details.

#### `--test-shard`#

Added in: v20.5.0, v18.19.0

Test suite shard to execute in a format of `<index>/<total>`, where

- `index` is a positive integer, index of divided parts.
- `total` is a positive integer, total of divided part.

This command will divide all tests files into `total` equal parts, and will run only those that happen to be in an `index` part.

For example, to split your tests suite into three parts, use this:

    node --test --test-shard=1/3
    node --test --test-shard=2/3
    node --test --test-shard=3/3

#### `--test-skip-pattern`#

Added in: v22.1.0

A regular expression that configures the test runner to skip tests whose name matches the provided pattern. See the documentation on filtering tests by name for more details.

If both `--test-name-pattern` and `--test-skip-pattern` are supplied, tests must satisfy both requirements in order to be executed.

#### `--test-timeout`#

Added in: v21.2.0, v20.11.0

A number of milliseconds the test execution will fail after. If unspecified, subtests inherit this value from their parent. The default value is `Infinity`.

#### `--test-update-snapshots`#

History

Version | Changes
--- | ---
v23.4.0, v22.13.0 | Snapshot testing is no longer experimental.
v22.3.0 | Added in: v22.3.0

Regenerates the snapshot files used by the test runner for snapshot testing.

#### `--throw-deprecation`#

Added in: v0.11.14

Throw errors for deprecations.

#### `--title=title`#

Added in: v10.7.0

Set `process.title` on startup.

#### `--tls-cipher-list=list`#

Added in: v4.0.0

Specify an alternative default TLS cipher list. Requires Node.js to be built with crypto support (default).

#### `--tls-keylog=file`#

Added in: v13.2.0, v12.16.0

Log TLS key material to a file. The key material is in NSS `SSLKEYLOGFILE` format and can be used by software (such as Wireshark) to decrypt the TLS traffic.

#### `--tls-max-v1.2`#

Added in: v12.0.0, v10.20.0

Set `tls.DEFAULT_MAX_VERSION` to 'TLSv1.2'. Use to disable support for TLSv1.3.

#### `--tls-max-v1.3`#

Added in: v12.0.0

Set default `tls.DEFAULT_MAX_VERSION` to 'TLSv1.3'. Use to enable support for TLSv1.3.

#### `--tls-min-v1.0`#

Added in: v12.0.0, v10.20.0

Set default `tls.DEFAULT_MIN_VERSION` to 'TLSv1'. Use for compatibility with old TLS clients or servers.

#### `--tls-min-v1.1`#

Added in: v12.0.0, v10.20.0

Set default `tls.DEFAULT_MIN_VERSION` to 'TLSv1.1'. Use for compatibility with old TLS clients or servers.

#### `--tls-min-v1.2`#

Added in: v12.2.0, v10.20.0

Set default `tls.DEFAULT_MIN_VERSION` to 'TLSv1.2'. This is the default for 12.x and later, but the option is supported for compatibility with older Node.js versions.

#### `--tls-min-v1.3`#

Added in: v12.0.0

Set default `tls.DEFAULT_MIN_VERSION` to 'TLSv1.3'. Use to disable support for TLSv1.2, which is not as secure as TLSv1.3.

#### `--trace-deprecation`#

Added in: v0.8.0

Print stack traces for deprecations.

#### `--trace-env`#

Added in: v23.4.0, v22.13.0

Print information about any access to environment variables done in the current Node.js instance to stderr, including:

- The environment variable reads that Node.js does internally.
- Writes in the form of `process.env.KEY = "SOME VALUE"`.
- Reads in the form of `process.env.KEY`.
- Definitions in the form of `Object.defineProperty(process.env, 'KEY', {...})`.
- Queries in the form of `Object.hasOwn(process.env, 'KEY')`, `process.env.hasOwnProperty('KEY')` or `'KEY' in process.env`.
- Deletions in the form of `delete process.env.KEY`.
- Enumerations inf the form of `...process.env` or `Object.keys(process.env)`.

Only the names of the environment variables being accessed are printed. The values are not printed.

To print the stack trace of the access, use `--trace-env-js-stack` and/or `--trace-env-native-stack`.

#### `--trace-env-js-stack`#

Added in: v23.4.0, v22.13.0

In addition to what `--trace-env` does, this prints the JavaScript stack trace of the access.

#### `--trace-env-native-stack`#

Added in: v23.4.0, v22.13.0

In addition to what `--trace-env` does, this prints the native stack trace of the access.

#### `--trace-event-categories`#

Added in: v7.7.0

A comma separated list of categories that should be traced when trace event tracing is enabled using `--trace-events-enabled`.

#### `--trace-event-file-pattern`#

Added in: v9.8.0

Template string specifying the filepath for the trace event data, it supports `${rotation}` and `${pid}`.

#### `--trace-events-enabled`#

Added in: v7.7.0

Enables the collection of trace event tracing information.

#### `--trace-exit`#

Added in: v13.5.0, v12.16.0

Prints a stack trace whenever an environment is exited proactively, i.e. invoking `process.exit()`.

#### `--trace-require-module=mode`#

Added in: v23.5.0, v22.13.0, v20.19.0

Prints information about usage of Loading ECMAScript modules using `require()`.

When `mode` is `all`, all usage is printed. When `mode` is `no-node-modules`, usage from the `node_modules` folder is excluded.

#### `--trace-sigint`#

Added in: v13.9.0, v12.17.0

Prints a stack trace on SIGINT.

#### `--trace-sync-io`#

Added in: v2.1.0

Prints a stack trace whenever synchronous I/O is detected after the first turn of the event loop.

#### `--trace-tls`#

Added in: v12.2.0

Prints TLS packet trace information to `stderr`. This can be used to debug TLS connection problems.

#### `--trace-uncaught`#

Added in: v13.1.0

Print stack traces for uncaught exceptions; usually, the stack trace associated with the creation of an `Error` is printed, whereas this makes Node.js also print the stack trace associated with throwing the value (which does not need to be an `Error` instance).

Enabling this option may affect garbage collection behavior negatively.

#### `--trace-warnings`#

Added in: v6.0.0

Print stack traces for process warnings (including deprecations).

#### `--track-heap-objects`#

Added in: v2.4.0

Track heap object allocations for heap snapshots.

#### `--unhandled-rejections=mode`#

History

Version | Changes
--- | ---
v15.0.0 | Changed default mode to `throw`. Previously, a warning was emitted.
v12.0.0, v10.17.0 | Added in: v12.0.0, v10.17.0

Using this flag allows to change what should happen when an unhandled rejection occurs. One of the following modes can be chosen:

- `throw`: Emit `unhandledRejection`. If this hook is not set, raise the unhandled rejection as an uncaught exception. This is the default.
- `strict`: Raise the unhandled rejection as an uncaught exception. If the exception is handled, `unhandledRejection` is emitted.
- `warn`: Always trigger a warning, no matter if the `unhandledRejection` hook is set or not but do not print the deprecation warning.
- `warn-with-error-code`: Emit `unhandledRejection`. If this hook is not set, trigger a warning, and set the process exit code to 1.
- `none`: Silence all warnings.

If a rejection happens during the command line entry point's ES module static loading phase, it will always raise it as an uncaught exception.

#### `--use-bundled-ca`, `--use-openssl-ca`#

Added in: v6.11.0

Use bundled Mozilla CA store as supplied by current Node.js version or use OpenSSL's default CA store. The default store is selectable at build-time.

The bundled CA store, as supplied by Node.js, is a snapshot of Mozilla CA store that is fixed at release time. It is identical on all supported platforms.

Using OpenSSL store allows for external modifications of the store. For most Linux and BSD distributions, this store is maintained by the distribution maintainers and system administrators. OpenSSL CA store location is dependent on configuration of the OpenSSL library but this can be altered at runtime using environment variables.

See `SSL_CERT_DIR` and `SSL_CERT_FILE`.

#### `--use-env-proxy`#

Added in: v24.5.0

Stability: 1.1 - Active Development

When enabled, Node.js parses the `HTTP_PROXY`, `HTTPS_PROXY` and `NO_PROXY` environment variables during startup, and tunnels requests over the specified proxy.

This is equivalent to setting the `NODE_USE_ENV_PROXY=1` environment variable. When both are set, `--use-env-proxy` takes precedence.

#### `--use-largepages=mode`#

Added in: v13.6.0, v12.17.0

Re-map the Node.js static code to large memory pages at startup. If supported on the target system, this will cause the Node.js static code to be moved onto 2 MiB pages instead of 4 KiB pages.

The following values are valid for `mode`:

- `off`: No mapping will be attempted. This is the default.
- `on`: If supported by the OS, mapping will be attempted. Failure to map will be ignored and a message will be printed to standard error.
- `silent`: If supported by the OS, mapping will be attempted. Failure to map will be ignored and will not be reported.

#### `--use-system-ca`#

History

Version | Changes
--- | ---
v23.9.0 | Added support on non-Windows and non-macOS.
v23.8.0 | Added in: v23.8.0

Node.js uses the trusted CA certificates present in the system store along with the `--use-bundled-ca` option and the `NODE_EXTRA_CA_CERTS` environment variable. On platforms other than Windows and macOS, this loads certificates from the directory and file trusted by OpenSSL, similar to `--use-openssl-ca`, with the difference being that it caches the certificates after first load.

On Windows and macOS, the certificate trust policy is similar to Chromium's policy for locally trusted certificates, but with some differences:

On macOS, the following settings are respected:

- Default and System Keychains
  - Trust:
    - Any certificate where the “When using this certificate” flag is set to “Always Trust” or
    - Any certificate where the “Secure Sockets Layer (SSL)” flag is set to “Always Trust”.
  - The certificate must also be valid, with "X.509 Basic Policy" set to “Always Trust”.

On Windows, the following settings are respected:

- Local Machine (accessed via `certlm.msc`)
  - Trust:
    - Trusted Root Certification Authorities
    - Trusted People
    - Enterprise Trust -> Enterprise -> Trusted Root Certification Authorities
    - Enterprise Trust -> Enterprise -> Trusted People
    - Enterprise Trust -> Group Policy -> Trusted Root Certification Authorities
    - Enterprise Trust -> Group Policy -> Trusted People
- Current User (accessed via `certmgr.msc`)
  - Trust:
    - Trusted Root Certification Authorities
    - Enterprise Trust -> Group Policy -> Trusted Root Certification Authorities

On Windows and macOS, Node.js would check that the user settings for the trusted certificates do not forbid them for TLS server authentication before using them.

Node.js currently does not support distrust/revocation of certificates from another source based on system settings.

On other systems, Node.js loads certificates from the default certificate file (typically `/etc/ssl/cert.pem`) and default certificate directory (typically `/etc/ssl/certs`) that the version of OpenSSL that Node.js links to respects. This typically works with the convention on major Linux distributions and other Unix-like systems. If the overriding OpenSSL environment variables (typically `SSL_CERT_FILE` and `SSL_CERT_DIR`, depending on the configuration of the OpenSSL that Node.js links to) are set, the specified paths will be used to load certificates instead. These environment variables can be used as workarounds if the conventional paths used by the version of OpenSSL Node.js links to are not consistent with the system configuration that the users have for some reason.

#### `--v8-options`#

Added in: v0.1.3

Print V8 command-line options.

#### `--v8-pool-size=num`#

Added in: v5.10.0

Set V8's thread pool size which will be used to allocate background jobs.

If set to `0` then Node.js will choose an appropriate size of the thread pool based on an estimate of the amount of parallelism.

The amount of parallelism refers to the number of computations that can be carried out simultaneously in a given machine. In general, it's the same as the amount of CPUs, but it may diverge in environments such as VMs or containers.

#### `-v`, `--version`#

Added in: v0.1.3

Print node's version.

#### `--watch`#

History

Version | Changes
--- | ---
v22.0.0, v20.13.0 | Watch mode is now stable.
v19.2.0, v18.13.0 | Test runner now supports running in watch mode.
v18.11.0, v16.19.0 | Added in: v18.11.0, v16.19.0

Starts Node.js in watch mode. When in watch mode, changes in the watched files cause the Node.js process to restart. By default, watch mode will watch the entry point and any required or imported module. Use `--watch-path` to specify what paths to watch.

This flag cannot be combined with `--check`, `--eval`, `--interactive`, or the REPL.

Note: The `--watch` flag requires a file path as an argument and is incompatible with `--run` or inline script input, as `--run` takes precedence and ignores watch mode. If no file is provided, Node.js will exit with status code `9`.

    node --watch index.js

#### `--watch-kill-signal`#

Added in: v24.4.0

Stability: 1.1 - Active Development

Customizes the signal sent to the process on watch mode restarts.

    node --watch --watch-kill-signal SIGINT test.js

#### `--watch-path`#

History

Version | Changes
--- | ---
v22.0.0, v20.13.0 | Watch mode is now stable.
v18.11.0, v16.19.0 | Added in: v18.11.0, v16.19.0

Starts Node.js in watch mode and specifies what paths to watch. When in watch mode, changes in the watched paths cause the Node.js process to restart. This will turn off watching of required or imported modules, even when used in combination with `--watch`.

This flag cannot be combined with `--check`, `--eval`, `--interactive`, `--test`, or the REPL.

Note: Using `--watch-path` implicitly enables `--watch`, which requires a file path and is incompatible with `--run`, as `--run` takes precedence and ignores watch mode.

    node --watch-path=./src --watch-path=./tests index.js

This option is only supported on macOS and Windows. An `ERR_FEATURE_UNAVAILABLE_ON_PLATFORM` exception will be thrown when the option is used on a platform that does not support it.

#### `--watch-preserve-output`#

Added in: v19.3.0, v18.13.0

Disable the clearing of the console when watch mode restarts the process.

    node --watch --watch-preserve-output test.js

#### `--zero-fill-buffers`#

Added in: v6.0.0

Automatically zero-fills all newly allocated `Buffer` and `SlowBuffer` instances.

### Environment variables#

Stability: 2 - Stable

#### `FORCE_COLOR=[1, 2, 3]`#

The `FORCE_COLOR` environment variable is used to enable ANSI colorized output. The value may be:

- `1`, `true`, or the empty string `''` indicate 16-color support,
- `2` to indicate 256-color support, or
- `3` to indicate 16 million-color support.

When `FORCE_COLOR` is used and set to a supported value, both the `NO_COLOR`, and `NODE_DISABLE_COLORS` environment variables are ignored.

Any other value will result in colorized output being disabled.

#### `NODE_COMPILE_CACHE=dir`#

Added in: v22.1.0

Stability: 1.1 - Active Development

Enable the module compile cache for the Node.js instance. See the documentation of module compile cache for details.

#### `NODE_COMPILE_CACHE_PORTABLE=1`#

When set to 1, the module compile cache can be reused across different directory locations as long as the module layout relative to the cache directory remains the same.

#### `NODE_DEBUG=module[,…]`#

Added in: v0.1.32

`','`-separated list of core modules that should print debug information.

#### `NODE_DEBUG_NATIVE=module[,…]`#

`','`-separated list of core C++ modules that should print debug information.

#### `NODE_DISABLE_COLORS=1`#

Added in: v0.3.0

When set, colors will not be used in the REPL.

#### `NODE_DISABLE_COMPILE_CACHE=1`#

Added in: v22.8.0

Stability: 1.1 - Active Development

Disable the module compile cache for the Node.js instance. See the documentation of module compile cache for details.

#### `NODE_EXTRA_CA_CERTS=file`#

Added in: v7.3.0

When set, the well known "root" CAs (like VeriSign) will be extended with the extra certificates in `file`. The file should consist of one or more trusted certificates in PEM format. A message will be emitted (once) with `process.emitWarning()` if the file is missing or malformed, but any errors are otherwise ignored.

Neither the well known nor extra certificates are used when the `ca` options property is explicitly specified for a TLS or HTTPS client or server.

This environment variable is ignored when `node` runs as setuid root or has Linux file capabilities set.

The `NODE_EXTRA_CA_CERTS` environment variable is only read when the Node.js process is first launched. Changing the value at runtime using `process.env.NODE_EXTRA_CA_CERTS` has no effect on the current process.

#### `NODE_ICU_DATA=file`#

Added in: v0.11.15

Data path for ICU (`Intl` object) data. Will extend linked-in data when compiled with small-icu support.

#### `NODE_NO_WARNINGS=1`#

Added in: v6.11.0

When set to `1`, process warnings are silenced.

#### `NODE_OPTIONS=options...`#

Added in: v8.0.0

A space-separated list of command-line options. `options...` are interpreted before command-line options, so command-line options will override or compound after anything in `options...`. Node.js will exit with an error if an option that is not allowed in the environment is used, such as `-p` or a script file.

If an option value contains a space, it can be escaped using double quotes:

    NODE_OPTIONS='--require "./my path/file.js"'

A singleton flag passed as a command-line option will override the same flag passed into `NODE_OPTIONS`:

    # The inspector will be available on port 5555
    NODE_OPTIONS='--inspect=localhost:4444' node --inspect=localhost:5555

A flag that can be passed multiple times will be treated as if its `NODE_OPTIONS` instances were passed first, and then its command-line instances afterwards:

    NODE_OPTIONS='--require "./a.js"' node --require "./b.js"
    # is equivalent to:
    node --require "./a.js" --require "./b.js"

Node.js options that are allowed are in the following list. If an option supports both --XX and --no-XX variants, they are both supported but only one is included in the list below.

- `--allow-addons`
- `--allow-child-process`
- `--allow-fs-read`
- `--allow-fs-write`
- `--allow-inspector`
- `--allow-wasi`
- `--allow-worker`
- `--conditions`, `-C`
- `--cpu-prof-dir`
- `--cpu-prof-interval`
- `--cpu-prof-name`
- `--cpu-prof`
- `--diagnostic-dir`
- `--disable-proto`
- `--disable-sigusr1`
- `--disable-warning`
- `--disable-wasm-trap-handler`
- `--dns-result-order`
- `--enable-fips`
- `--enable-network-family-autoselection`
- `--enable-source-maps`
- `--entry-url`
- `--experimental-abortcontroller`
- `--experimental-addon-modules`
- `--experimental-detect-module`
- `--experimental-eventsource`
- `--experimental-import-meta-resolve`
- `--experimental-json-modules`
- `--experimental-loader`
- `--experimental-modules`
- `--experimental-print-required-tla`
- `--experimental-require-module`
- `--experimental-shadow-realm`
- `--experimental-specifier-resolution`
- `--experimental-test-isolation`
- `--experimental-top-level-await`
- `--experimental-transform-types`
- `--experimental-vm-modules`
- `--experimental-wasi-unstable-preview1`
- `--experimental-webstorage`
- `--force-context-aware`
- `--force-fips`
- `--force-node-api-uncaught-exceptions-policy`
- `--frozen-intrinsics`
- `--heap-prof-dir`
- `--heap-prof-interval`
- `--heap-prof-name`
- `--heap-prof`
- `--heapsnapshot-near-heap-limit`
- `--heapsnapshot-signal`
- `--http-parser`
- `--icu-data-dir`
- `--import`
- `--input-type`
- `--insecure-http-parser`
- `--inspect-brk`
- `--inspect-port`, `--debug-port`
- `--inspect-publish-uid`
- `--inspect-wait`
- `--inspect`
- `--localstorage-file`
- `--max-http-header-size`
- `--max-old-space-size-percentage`
- `--napi-modules`
- `--network-family-autoselection-attempt-timeout`
- `--no-addons`
- `--no-async-context-frame`
- `--no-deprecation`
- `--no-experimental-global-navigator`
- `--no-experimental-repl-await`
- `--no-experimental-sqlite`
- `--no-experimental-strip-types`
- `--no-experimental-websocket`
- `--no-extra-info-on-fatal-exception`
- `--no-force-async-hooks-checks`
- `--no-global-search-paths`
- `--no-network-family-autoselection`
- `--no-strip-types`
- `--no-warnings`
- `--node-memory-debug`
- `--openssl-config`
- `--openssl-legacy-provider`
- `--openssl-shared-config`
- `--pending-deprecation`
- `--permission`
- `--preserve-symlinks-main`
- `--preserve-symlinks`
- `--prof-process`
- `--redirect-warnings`
- `--report-compact`
- `--report-dir`, `--report-directory`
- `--report-exclude-env`
- `--report-exclude-network`
- `--report-filename`
- `--report-on-fatalerror`
- `--report-on-signal`
- `--report-signal`
- `--report-uncaught-exception`
- `--require`, `-r`
- `--secure-heap-min`
- `--secure-heap`
- `--snapshot-blob`
- `--test-coverage-branches`
- `--test-coverage-exclude`
- `--test-coverage-functions`
- `--test-coverage-include`
- `--test-coverage-lines`
- `--test-global-setup`
- `--test-isolation`
- `--test-name-pattern`
- `--test-only`
- `--test-reporter-destination`
- `--test-reporter`
- `--test-rerun-failures`
- `--test-shard`
- `--test-skip-pattern`
- `--throw-deprecation`
- `--title`
- `--tls-cipher-list`
- `--tls-keylog`
- `--tls-max-v1.2`
- `--tls-max-v1.3`
- `--tls-min-v1.0`
- `--tls-min-v1.1`
- `--tls-min-v1.2`
- `--tls-min-v1.3`
- `--trace-deprecation`
- `--trace-env-js-stack`
- `--trace-env-native-stack`
- `--trace-env`
- `--trace-event-categories`
- `--trace-event-file-pattern`
- `--trace-events-enabled`
- `--trace-exit`
- `--trace-require-module`
- `--trace-sigint`
- `--trace-sync-io`
- `--trace-tls`
- `--trace-uncaught`
- `--trace-warnings`
- `--track-heap-objects`
- `--unhandled-rejections`
- `--use-bundled-ca`
- `--use-env-proxy`
- `--use-largepages`
- `--use-openssl-ca`
- `--use-system-ca`
- `--v8-pool-size`
- `--watch-kill-signal`
- `--watch-path`
- `--watch-preserve-output`
- `--watch`
- `--zero-fill-buffers`

V8 options that are allowed are:

- `--abort-on-uncaught-exception`
- `--disallow-code-generation-from-strings`
- `--enable-etw-stack-walking`
- `--expose-gc`
- `--interpreted-frames-native-stack`
- `--jitless`
- `--max-old-space-size`
- `--max-semi-space-size`
- `--perf-basic-prof-only-functions`
- `--perf-basic-prof`
- `--perf-prof-unwinding-info`
- `--perf-prof`
- `--stack-trace-limit`

`--perf-basic-prof-only-functions`, `--perf-basic-prof`, `--perf-prof-unwinding-info`, and `--perf-prof` are only available on Linux.

`--enable-etw-stack-walking` is only available on Windows.

#### `NODE_PATH=path[:…]`#

Added in: v0.1.32

`':'`-separated list of directories prefixed to the module search path.

On Windows, this is a `';'`-separated list instead.

#### `NODE_PENDING_DEPRECATION=1`#

Added in: v8.0.0

When set to `1`, emit pending deprecation warnings.

Pending deprecations are generally identical to a runtime deprecation with the notable exception that they are turned off by default and will not be emitted unless either the `--pending-deprecation` command-line flag, or the `NODE_PENDING_DEPRECATION=1` environment variable, is set. Pending deprecations are used to provide a kind of selective "early warning" mechanism that developers may leverage to detect deprecated API usage.

#### `NODE_PENDING_PIPE_INSTANCES=instances`#

Set the number of pending pipe instance handles when the pipe server is waiting for connections. This setting applies to Windows only.

#### `NODE_PRESERVE_SYMLINKS=1`#

Added in: v7.1.0

When set to `1`, instructs the module loader to preserve symbolic links when resolving and caching modules.

#### `NODE_REDIRECT_WARNINGS=file`#

Added in: v8.0.0

When set, process warnings will be emitted to the given file instead of printing to stderr. The file will be created if it does not exist, and will be appended to if it does. If an error occurs while attempting to write the warning to the file, the warning will be written to stderr instead. This is equivalent to using the `--redirect-warnings=file` command-line flag.

#### `NODE_REPL_EXTERNAL_MODULE=file`#

History

Version | Changes
--- | ---
v22.3.0, v20.16.0 | Remove the possibility to use this env var with kDisableNodeOptionsEnv for embedders.
v13.0.0, v12.16.0 | Added in: v13.0.0, v12.16.0

Path to a Node.js module which will be loaded in place of the built-in REPL. Overriding this value to an empty string (`''`) will use the built-in REPL.

#### `NODE_REPL_HISTORY=file`#

Added in: v3.0.0

Path to the file used to store the persistent REPL history. The default path is `~/.node_repl_history`, which is overridden by this variable. Setting the value to an empty string (`''` or `' '`) disables persistent REPL history.

#### `NODE_SKIP_PLATFORM_CHECK=value`#

Added in: v14.5.0

If `value` equals `'1'`, the check for a supported platform is skipped during Node.js startup. Node.js might not execute correctly. Any issues encountered on unsupported platforms will not be fixed.

#### `NODE_TEST_CONTEXT=value`#

If `value` equals `'child'`, test reporter options will be overridden and test output will be sent to stdout in the TAP format. If any other value is provided, Node.js makes no guarantees about the reporter format used or its stability.

#### `NODE_TLS_REJECT_UNAUTHORIZED=value`#

If `value` equals `'0'`, certificate validation is disabled for TLS connections. This makes TLS, and HTTPS by extension, insecure. The use of this environment variable is strongly discouraged.

#### `NODE_USE_ENV_PROXY=1`#

Added in: v24.0.0

Stability: 1.1 - Active Development

When enabled, Node.js parses the `HTTP_PROXY`, `HTTPS_PROXY` and `NO_PROXY` environment variables during startup, and tunnels requests over the specified proxy.

This can also be enabled using the `--use-env-proxy` command-line flag. When both are set, `--use-env-proxy` takes precedence.

#### `NODE_USE_SYSTEM_CA=1`#

Added in: v24.6.0

Node.js uses the trusted CA certificates present in the system store along with the `--use-bundled-ca` option and the `NODE_EXTRA_CA_CERTS` environment variable.

This can also be enabled using the `--use-system-ca` command-line flag. When both are set, `--use-system-ca` takes precedence.

#### `NODE_V8_COVERAGE=dir`#

When set, Node.js will begin outputting V8 JavaScript code coverage and Source Map data to the directory provided as an argument (coverage information is written as JSON to files with a `coverage` prefix).

`NODE_V8_COVERAGE` will automatically propagate to subprocesses, making it easier to instrument applications that call the `child_process.spawn()` family of functions. `NODE_V8_COVERAGE` can be set to an empty string, to prevent propagation.

##### Coverage output#

Coverage is output as an array of ScriptCoverage objects on the top-level key `result`:

    {
      "result": [
        {
          "scriptId": "67",
          "url": "internal/tty.js",
          "functions": []
        }
      ]
    }

##### Source map cache#

Stability: 1 - Experimental

If found, source map data is appended to the top-level key `source-map-cache` on the JSON coverage object.

`source-map-cache` is an object with keys representing the files source maps were extracted from, and values which include the raw source-map URL (in the key `url`), the parsed Source Map v3 information (in the key `data`), and the line lengths of the source file (in the key `lineLengths`).

    {
      "result": [
        {
          "scriptId": "68",
          "url": "file:///absolute/path/to/source.js",
          "functions": []
        }
      ],
      "source-map-cache": {
        "file:///absolute/path/to/source.js": {
          "url": "./path-to-map.json",
          "data": {
            "version": 3,
            "sources": [
              "file:///absolute/path/to/original.js"
            ],
            "names": [
              "Foo",
              "console",
              "info"
            ],
            "mappings": "MAAMA,IACJC,YAAaC",
            "sourceRoot": "./"
          },
          "lineLengths": [
            13,
            62,
            38,
            27
          ]
        }
      }
    }

#### `NO_COLOR=<any>`#

`NO_COLOR` is an alias for `NODE_DISABLE_COLORS`. The value of the environment variable is arbitrary.

#### `OPENSSL_CONF=file`#

Added in: v6.11.0

Load an OpenSSL configuration file on startup. Among other uses, this can be used to enable FIPS-compliant crypto if Node.js is built with `./configure --openssl-fips`.

If the `--openssl-config` command-line option is used, the environment variable is ignored.

#### `SSL_CERT_DIR=dir`#

Added in: v7.7.0

If `--use-openssl-ca` is enabled, or if `--use-system-ca` is enabled on platforms other than macOS and Windows, this overrides and sets OpenSSL's directory containing trusted certificates.

Be aware that unless the child environment is explicitly set, this environment variable will be inherited by any child processes, and if they use OpenSSL, it may cause them to trust the same CAs as node.

#### `SSL_CERT_FILE=file`#

Added in: v7.7.0

If `--use-openssl-ca` is enabled, or if `--use-system-ca` is enabled on platforms other than macOS and Windows, this overrides and sets OpenSSL's file containing trusted certificates.

Be aware that unless the child environment is explicitly set, this environment variable will be inherited by any child processes, and if they use OpenSSL, it may cause them to trust the same CAs as node.

#### `TZ`#

History

Version | Changes
--- | ---
v16.2.0 | Changing the TZ variable using process.env.TZ = changes the timezone on Windows as well.
v13.0.0 | Changing the TZ variable using process.env.TZ = changes the timezone on POSIX systems.
v0.0.1 | Added in: v0.0.1

The `TZ` environment variable is used to specify the timezone configuration.

While Node.js does not support all of the various ways that `TZ` is handled in other environments, it does support basic timezone IDs (such as `'Etc/UTC'`, `'Europe/Paris'`, or `'America/New_York'`). It may support a few other abbreviations or aliases, but these are strongly discouraged and not guaranteed.

    $ TZ=Europe/Dublin node -pe "new Date().toString()"
    Wed May 12 2021 20:30:48 GMT+0100 (Irish Standard Time)

#### `UV_THREADPOOL_SIZE=size`#

Set the number of threads used in libuv's threadpool to `size` threads.

Asynchronous system APIs are used by Node.js whenever possible, but where they do not exist, libuv's threadpool is used to create asynchronous node APIs based on synchronous system APIs. Node.js APIs that use the threadpool are:

- all `fs` APIs, other than the file watcher APIs and those that are explicitly synchronous
- asynchronous crypto APIs such as `crypto.pbkdf2()`, `crypto.scrypt()`, `crypto.randomBytes()`, `crypto.randomFill()`, `crypto.generateKeyPair()`
- `dns.lookup()`
- all `zlib` APIs, other than those that are explicitly synchronous

Because libuv's threadpool has a fixed size, it means that if for whatever reason any of these APIs takes a long time, other (seemingly unrelated) APIs that run in libuv's threadpool will experience degraded performance. In order to mitigate this issue, one potential solution is to increase the size of libuv's threadpool by setting the `'UV_THREADPOOL_SIZE'` environment variable to a value greater than `4` (its current default value). However, setting this from inside the process using `process.env.UV_THREADPOOL_SIZE=size` is not guranteed to work as the threadpool would have been created as part of the runtime initialisation much before user code is run. For more information, see the libuv threadpool documentation.

### Useful V8 options#

V8 has its own set of CLI options. Any V8 CLI option that is provided to `node` will be passed on to V8 to handle. V8's options have no stability guarantee. The V8 team themselves don't consider them to be part of their formal API, and reserve the right to change them at any time. Likewise, they are not covered by the Node.js stability guarantees. Many of the V8 options are of interest only to V8 developers. Despite this, there is a small set of V8 options that are widely applicable to Node.js, and they are documented here:

#### `--abort-on-uncaught-exception`#

#### `--disallow-code-generation-from-strings`#

#### `--enable-etw-stack-walking`#

#### `--expose-gc`#

#### `--harmony-shadow-realm`#

#### `--heap-snapshot-on-oom`#

#### `--interpreted-frames-native-stack`#

#### `--jitless`#

#### `--max-old-space-size=SIZE` (in MiB)#

Sets the max memory size of V8's old memory section. As memory consumption approaches the limit, V8 will spend more time on garbage collection in an effort to free unused memory.

On a machine with 2 GiB of memory, consider setting this to 1536 (1.5 GiB) to leave some memory for other uses and avoid swapping.

    node --max-old-space-size=1536 index.js

#### `--max-semi-space-size=SIZE` (in MiB)#

Sets the maximum semi-space size for V8's scavenge garbage collector in MiB (mebibytes). Increasing the max size of a semi-space may improve throughput for Node.js at the cost of more memory consumption.

Since the young generation size of the V8 heap is three times (see `YoungGenerationSizeFromSemiSpaceSize` in V8) the size of the semi-space, an increase of 1 MiB to semi-space applies to each of the three individual semi-spaces and causes the heap size to increase by 3 MiB. The throughput improvement depends on your workload (see #42511).

The default value depends on the memory limit. For example, on 64-bit systems with a memory limit of 512 MiB, the max size of a semi-space defaults to 1 MiB. For memory limits up to and including 2GiB, the default max size of a semi-space will be less than 16 MiB on 64-bit systems.

To get the best configuration for your application, you should try different max-semi-space-size values when running benchmarks for your application.

For example, benchmark on a 64-bit systems:

    for MiB in 16 32 64 128; do
        node --max-semi-space-size=$MiB index.js
    done

#### `--perf-basic-prof`#

#### `--perf-basic-prof-only-functions`#

#### `--perf-prof`#

#### `--perf-prof-unwinding-info`#

#### `--prof`#

#### `--security-revert`#

#### `--stack-trace-limit=limit`#

The maximum number of stack frames to collect in an error's stack trace. Setting it to 0 disables stack trace collection. The default value is 10.

    node --stack-trace-limit=12 -p -e "Error.stackTraceLimit" # prints 12