nodejs/doc/api/cli.md

# Command-line API

<!--introduced_in=v5.9.1-->

<!--type=misc-->

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 path is then resolved by [CommonJS][] module loader, or by the
[ES module loader][Modules loaders] if [`--experimental-default-type=module`][]
is passed. If no corresponding file is found, an error is thrown.

If a file is found, its path will be passed to the
[ES module loader][Modules loaders] under any of the following conditions:

* The program was started with a command-line flag that forces the entry
  point to be loaded with ECMAScript module loader, such as `--import` or
  [`--experimental-default-type=module`][].
* The file has an `.mjs` 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"`.

Otherwise, the file is loaded using the CommonJS module loader. See
[Modules loaders][] for more details.

### ECMAScript modules loader entry point caveat

When loading, the [ES module loader][Modules loaders] loads the program
entry point, the `node` command will accept as input only files with `.js`,
`.mjs`, or `.cjs` extensions; with `.wasm` extensions when
[`--experimental-wasm-modules`][] is enabled; and with no extension when
[`--experimental-default-type=module`][] is passed.

## Options

<!-- YAML
changes:
  - version: v10.12.0
    pr-url: https://github.com/nodejs/node/pull/23020
    description: Underscores instead of dashes are now allowed for
                 Node.js options as well, in addition to V8 options.
-->

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.

### `-`

<!-- YAML
added: 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.

### `--`

<!-- YAML
added: 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`

<!-- YAML
added: 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`

<!-- YAML
added: REPLACEME
-->

> 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:

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

```console
$ node --experimental-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`

<!-- YAML
added: 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:

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

```console
$ node --experimental-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 Object.spawn (node:child_process:723:9)
    at Object.<anonymous> (/home/index.js:3:14)
    at Module._compile (node:internal/modules/cjs/loader:1120:14)
    at Module._extensions..js (node:internal/modules/cjs/loader:1174:10)
    at Module.load (node:internal/modules/cjs/loader:998:32)
    at Module._load (node:internal/modules/cjs/loader:839:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12)
    at node:internal/main/run_main_module:17:47 {
  code: 'ERR_ACCESS_DENIED',
  permission: 'ChildProcess'
}
```

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

<!-- YAML
added: v20.0.0
changes:
  - version: v20.7.0
    pr-url: https://github.com/nodejs/node/pull/49047
    description: Paths delimited by comma (`,`) are no longer allowed.
-->

> Stability: 1.1 - Active development

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/`

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.

Relative paths are NOT yet supported by the CLI flag.

The initializer module also needs to be allowed. Consider the following example:

```console
$ node --experimental-permission t.js
node:internal/modules/cjs/loader:162
  const result = internalModuleStat(filename);
                 ^

Error: Access to this API has been restricted
    at stat (node:internal/modules/cjs/loader:162:18)
    at Module._findPath (node:internal/modules/cjs/loader:640:16)
    at resolveMainPath (node:internal/modules/run_main:15:25)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:53:24)
    at node:internal/main/run_main_module:23:47 {
  code: 'ERR_ACCESS_DENIED',
  permission: 'FileSystemRead',
  resource: '/Users/rafaelgss/repos/os/node/t.js'
}
```

The process needs to have access to the `index.js` module:

```bash
node --experimental-permission --allow-fs-read=/path/to/index.js index.js
```

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

<!-- YAML
added: v20.0.0
changes:
  - version: v20.7.0
    pr-url: https://github.com/nodejs/node/pull/49047
    description: Paths delimited by comma (`,`) are no longer allowed.
-->

> Stability: 1.1 - Active development

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-read` flags.
  Example `--allow-fs-read=/folder1/ --allow-fs-read=/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.

Relative paths are NOT supported through the CLI flag.

### `--allow-worker`

<!-- YAML
added: 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:

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

```console
$ node --experimental-permission --allow-fs-read=* index.js
node:internal/worker:188
    this[kHandle] = new WorkerImpl(url,
                    ^

Error: Access to this API has been restricted
    at new Worker (node:internal/worker:188:21)
    at Object.<anonymous> (/home/index.js.js:3:1)
    at Module._compile (node:internal/modules/cjs/loader:1120:14)
    at Module._extensions..js (node:internal/modules/cjs/loader:1174:10)
    at Module.load (node:internal/modules/cjs/loader:998:32)
    at Module._load (node:internal/modules/cjs/loader:839:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12)
    at node:internal/main/run_main_module:17:47 {
  code: 'ERR_ACCESS_DENIED',
  permission: 'WorkerThreads'
}
```

### `--build-snapshot`

<!-- YAML
added: v18.8.0
-->

> Stability: 1 - Experimental

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`.

```console
$ 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:

```console
$ 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.

Currently the support for run-time snapshot is experimental in that:

1. User-land modules are not yet supported in the snapshot, so only
   one single file can be snapshotted. Users can bundle their applications
   into a single script with their bundler of choice before building
   a snapshot, however.
2. Only a subset of the built-in modules work in the snapshot, though the
   Node.js core test suite checks that a few fairly complex applications
   can be snapshotted. Support for more modules are being added. If any
   crashes or buggy behaviors occur when building a snapshot, please file
   a report in the [Node.js issue tracker][] and link to it in the
   [tracking issue for user-land snapshots][].

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

<!-- YAML
added: REPLACEME
-->

> Stability: 1 - Experimental

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`

<!-- YAML
added:
  - v5.0.0
  - v4.2.0
changes:
  - version: v10.0.0
    pr-url: https://github.com/nodejs/node/pull/19600
    description: The `--require` option is now supported when checking a file.
-->

Syntax check the script without executing.

### `--completion-bash`

<!-- YAML
added: v10.12.0
-->

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

```bash
node --completion-bash > node_bash_completion
source node_bash_completion
```

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

<!-- YAML
added:
  - v14.9.0
  - v12.19.0
-->

> Stability: 1 - Experimental

Enable experimental support for 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:

```bash
node -C development app.js
```

### `--cpu-prof`

<!-- YAML
added: v12.0.0
-->

> Stability: 1 - Experimental

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`.

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

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

<!-- YAML
added: v12.0.0
-->

> Stability: 1 - Experimental

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`

<!-- YAML
added: v12.2.0
-->

> Stability: 1 - Experimental

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

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

<!-- YAML
added: v12.0.0
-->

> Stability: 1 - Experimental

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-warning=code-or-type`

> Stability: 1.1 - Active development

<!-- YAML
added: v21.3.0
-->

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

Warnings emitted from [`process.emitWarning()`][emit_warning] 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')`][DEP0025 warning] when executed with
`node --disable-warning=DEP0025`:

```mjs
import sys from 'node:sys';
```

```cjs
const sys = require('node:sys');
```

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

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

vm.measureMemory();
```

```cjs
const sys = require('node:sys');
const vm = require('node:vm');

vm.measureMemory();
```

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

<!-- YAML
added:
 - 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`.

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

<!-- YAML
added: 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`

<!-- YAML
added:
  - v16.4.0
  - v14.18.0
changes:
  - version: v17.0.0
    pr-url: https://github.com/nodejs/node/pull/39987
    description: Changed default value to `verbatim`.
-->

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

* `ipv4first`: sets default `verbatim` `false`.
* `verbatim`: sets default `verbatim` `true`.

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

### `--enable-fips`

<!-- YAML
added: v6.0.0
-->

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

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

<!-- YAML
added: v18.18.0
-->

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

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

<!-- YAML
added: v12.12.0
changes:
  - version:
      - v15.11.0
      - v14.18.0
    pr-url: https://github.com/nodejs/node/pull/37362
    description: This API is no longer experimental.
-->

Enable [Source Map v3][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.

```js
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`.

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

> Stability: 1.1 - Active development

<!-- YAML
added: 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][environment_variables], 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.

```bash
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 `=`:

```text
PORT=3000
```

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

```text
# 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.

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

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

<!-- YAML
added: v0.5.2
changes:
  - version: v5.11.0
    pr-url: https://github.com/nodejs/node/pull/5348
    description: Built-in libraries are now available as predefined variables.
-->

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.

### `--experimental-default-type=type`

<!-- YAML
added:
  - v21.0.0
  - v20.10.0
  - v18.19.0
-->

> Stability: 1.0 - Early development

Define which module system, `module` or `commonjs`, to use for the following:

* String input provided via `--eval` or STDIN, if `--input-type` is unspecified.

* Files ending in `.js` or with no extension, if there is no `package.json` file
  present in the same folder or any parent folder.

* Files ending in `.js` or with no extension, if the nearest parent
  `package.json` field lacks a `"type"` field; unless the `package.json` folder
  or any parent folder is inside a `node_modules` folder.

In other words, `--experimental-default-type=module` flips all the places where
Node.js currently defaults to CommonJS to instead default to ECMAScript modules,
with the exception of folders and subfolders below `node_modules`, for backward
compatibility.

Under `--experimental-default-type=module` and `--experimental-wasm-modules`,
files with no extension will be treated as WebAssembly if they begin with the
WebAssembly magic number (`\0asm`); otherwise they will be treated as ES module
JavaScript.

### `--experimental-detect-module`

<!-- YAML
added:
  - v21.1.0
  - v20.10.0
-->

> Stability: 1.0 - Early development

Node.js will inspect the source code of ambiguous input to determine whether it
contains ES module syntax; if such syntax is detected, the input will be treated
as an ES module.

Ambiguous input is defined as:

* Files with a `.js` extension or no extension; and either no controlling
  `package.json` file or one that lacks a `type` field; and
  `--experimental-default-type` is not specified.
* String input (`--eval` or STDIN) when neither `--input-type` nor
  `--experimental-default-type` are specified.

ES module syntax is defined as syntax that would throw when evaluated as
CommonJS. This includes `import` and `export` statements and `import.meta`
references. It does _not_ include `import()` expressions, which are valid in
CommonJS.

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

<!-- YAML
added:
  - v13.9.0
  - v12.16.2
changes:
  - version:
    - v20.6.0
    - v18.19.0
    pr-url: https://github.com/nodejs/node/pull/49028
    description: synchronous import.meta.resolve made available by default, with
                 the flag retained for enabling the experimental second argument
                 as previously supported.
-->

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-loader=module`

<!-- YAML
added: v8.8.0
changes:
  - version: v12.11.1
    pr-url: https://github.com/nodejs/node/pull/29752
    description: This flag was renamed from `--loader` to
                 `--experimental-loader`.
-->

> This flag is discouraged and may be removed in a future version of Node.js.
> Please use
> [`--import` with `register()`][module customization hooks: enabling] instead.

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

### `--experimental-network-imports`

<!-- YAML
added:
  - v17.6.0
  - v16.15.0
-->

> Stability: 1 - Experimental

Enable experimental support for the `https:` protocol in `import` specifiers.

### `--experimental-permission`

<!-- YAML
added: v20.0.0
-->

> Stability: 1.1 - Active development

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

### `--experimental-policy`

<!-- YAML
added: v11.8.0
-->

Use the specified file as a security policy.

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

<!-- YAML
added: 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][`--experimental-sea-config`] for details.

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

<!-- YAML
added:
  - v19.0.0
  - v18.13.0
-->

Use this flag to enable [ShadowRealm][] support.

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

<!-- YAML
added:
  - v19.7.0
  - v18.15.0
changes:
  - version:
    - v20.1.0
    - v18.17.0
    pr-url: https://github.com/nodejs/node/pull/47686
    description: This option can be used with `--test`.
-->

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-vm-modules`

<!-- YAML
added: v9.6.0
-->

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

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

<!-- YAML
added:
  - v13.3.0
  - v12.16.0
changes:
  - version:
    - v20.0.0
    - v18.17.0
    pr-url: https://github.com/nodejs/node/pull/47286
    description: This option is no longer required as WASI is
                 enabled by default, but can still be passed.
  - version: v13.6.0
    pr-url: https://github.com/nodejs/node/pull/30980
    description: changed from `--experimental-wasi-unstable-preview0` to
                 `--experimental-wasi-unstable-preview1`.
-->

Enable experimental WebAssembly System Interface (WASI) support.

### `--experimental-wasm-modules`

<!-- YAML
added: v12.3.0
-->

Enable experimental WebAssembly module support.

### `--experimental-websocket`

<!-- YAML
added:
  - v21.0.0
  - v20.10.0
-->

Enable experimental [`WebSocket`][] support.

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

<!-- YAML
added: v12.12.0
-->

Disable loading native addons that are not [context-aware][].

### `--force-fips`

<!-- YAML
added: 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`

<!-- YAML
added:
  - 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`

<!-- YAML
added: 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`

<!-- YAML
added: v12.4.0
-->

> Stability: 1 - Experimental

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`.

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

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

<!-- YAML
added: v12.4.0
-->

> Stability: 1 - Experimental

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`

<!-- YAML
added: v12.4.0
-->

> Stability: 1 - Experimental

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

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

<!-- YAML
added: v12.4.0
-->

> Stability: 1 - Experimental

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

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

<!-- YAML
added:
  - v15.1.0
  - v14.18.0
-->

> Stability: 1 - Experimental

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.

```console
$ 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`

<!-- YAML
added: 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.

```console
$ 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`

<!-- YAML
added: v0.1.3
-->

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

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

<!-- YAML
added: v0.11.15
-->

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

### `--import=module`

<!-- YAML
added:
 - 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`.

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

<!-- YAML
added: v12.0.0
-->

This configures Node.js to interpret `--eval` or `STDIN` input as CommonJS or
as an ES module. Valid values are `"commonjs"` or `"module"`. The default is
`"commonjs"` unless [`--experimental-default-type=module`][] is used.

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`

<!-- YAML
added:
 - 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 trasfer 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[=[host:]port]`

<!-- YAML
added: v6.3.0
-->

Activate inspector on `host:port`. Default is `127.0.0.1:9229`.

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][].

<!-- Anchor to make sure old links find a target -->

<a id="inspector_security"></a>

#### 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.

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

<!-- YAML
added: v7.6.0
-->

Activate inspector on `host:port` and break at start of user script.
Default `host:port` is `127.0.0.1:9229`.

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

<!-- YAML
added: 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.

Default host is `127.0.0.1`.

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`.

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

<!-- YAML
added: v0.7.7
-->

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

### `--jitless`

<!-- YAML
added: v12.0.0
-->

Disable [runtime allocation of executable memory][jitless]. 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.

This flag is inherited from V8 and is subject to change upstream. It may
disappear in a non-semver-major release.

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

<!-- YAML
added:
 - v11.6.0
 - v10.15.0
changes:
  - version: v13.13.0
    pr-url: https://github.com/nodejs/node/pull/32520
    description: Change maximum default size of HTTP headers from 8 KiB to 16 KiB.
-->

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

### `--napi-modules`

<!-- YAML
added: v7.10.0
-->

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

### `--no-addons`

<!-- YAML
added:
  - 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-deprecation`

<!-- YAML
added: v0.8.0
-->

Silence deprecation warnings.

### `--no-experimental-fetch`

<!-- YAML
added: v18.0.0
-->

Disable exposition of [Fetch API][] on the global scope.

### `--no-experimental-global-customevent`

<!-- YAML
added: v19.0.0
-->

Disable exposition of [CustomEvent Web API][] on the global scope.

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

<!-- YAML
added: v21.2.0
-->

> Stability: 1 - Experimental

Disable exposition of [Navigator API][] on the global scope.

### `--no-experimental-global-webcrypto`

<!-- YAML
added: v19.0.0
-->

Disable exposition of [Web Crypto API][] on the global scope.

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

<!-- YAML
added: v16.6.0
-->

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

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

<!-- YAML
added: v17.0.0
-->

Hide extra information on fatal exception that causes exit.

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

<!-- YAML
added: v9.0.0
-->

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

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

<!-- YAML
added: v16.10.0
-->

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

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

<!-- YAML
added: v19.4.0
changes:
  - version: v20.0.0
    pr-url: https://github.com/nodejs/node/pull/46790
    description: The flag was renamed from `--no-enable-network-family-autoselection`
                 to `--no-network-family-autoselection`. The old name can still work as
                 an alias.
-->

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

### `--no-warnings`

<!-- YAML
added: v6.0.0
-->

Silence all process warnings (including deprecations).

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

<!-- YAML
added:
  - 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`

<!-- YAML
added: 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`

<!-- YAML
added:
  - v17.0.0
  - v16.17.0
-->

Enable OpenSSL 3.0 legacy provider. For more information please see
[OSSL\_PROVIDER-legacy][OSSL_PROVIDER-legacy].

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

<!-- YAML
added:
  - 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`

<!-- YAML
added: 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.

### `--policy-integrity=sri`

<!-- YAML
added: v12.7.0
-->

> Stability: 1 - Experimental

Instructs Node.js to error prior to running any code if the policy does not have
the specified integrity. It expects a [Subresource Integrity][] string as a
parameter.

### `--preserve-symlinks`

<!-- YAML
added: 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:

```text
{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`

<!-- YAML
added: 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"`

<!-- YAML
added: v0.6.4
changes:
  - version: v5.11.0
    pr-url: https://github.com/nodejs/node/pull/5348
    description: Built-in libraries are now available as predefined variables.
-->

Identical to `-e` but prints the result.

### `--prof`

<!-- YAML
added: v2.0.0
-->

Generate V8 profiler output.

### `--prof-process`

<!-- YAML
added: v5.2.0
-->

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

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

<!-- YAML
added: 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`

<!-- YAML
added:
 - 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`

<!-- YAML
added: v11.8.0
changes:
  - version:
     - v13.12.0
     - v12.17.0
    pr-url: https://github.com/nodejs/node/pull/32242
    description: This option is no longer experimental.
  - version: v12.0.0
    pr-url: https://github.com/nodejs/node/pull/27312
    description: Changed from `--diagnostic-report-directory` to
                 `--report-directory`.
-->

Location at which the report will be generated.

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

<!-- YAML
added: v11.8.0
changes:
  - version:
     - v13.12.0
     - v12.17.0
    pr-url: https://github.com/nodejs/node/pull/32242
    description: This option is no longer experimental.
  - version: v12.0.0
    pr-url: https://github.com/nodejs/node/pull/27312
    description: changed from `--diagnostic-report-filename` to
                 `--report-filename`.
-->

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`

<!-- YAML
added: v11.8.0
changes:
  - version:
    - v14.0.0
    - v13.14.0
    - v12.17.0
    pr-url: https://github.com/nodejs/node/pull/32496
    description: This option is no longer experimental.
  - version: v12.0.0
    pr-url: https://github.com/nodejs/node/pull/27312
    description: changed from `--diagnostic-report-on-fatalerror` to
                 `--report-on-fatalerror`.
-->

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`

<!-- YAML
added: v11.8.0
changes:
  - version:
     - v13.12.0
     - v12.17.0
    pr-url: https://github.com/nodejs/node/pull/32242
    description: This option is no longer experimental.
  - version: v12.0.0
    pr-url: https://github.com/nodejs/node/pull/27312
    description: changed from `--diagnostic-report-on-signal` to
                 `--report-on-signal`.
-->

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`

<!-- YAML
added: v11.8.0
changes:
  - version:
     - v13.12.0
     - v12.17.0
    pr-url: https://github.com/nodejs/node/pull/32242
    description: This option is no longer experimental.
  - version: v12.0.0
    pr-url: https://github.com/nodejs/node/pull/27312
    description: changed from `--diagnostic-report-signal` to
                 `--report-signal`.
-->

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

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

<!-- YAML
added: v11.8.0
changes:
  - version:
      - v18.8.0
      - v16.18.0
    pr-url: https://github.com/nodejs/node/pull/44208
    description: Report is not generated if the uncaught exception is handled.
  - version:
     - v13.12.0
     - v12.17.0
    pr-url: https://github.com/nodejs/node/pull/32242
    description: This option is no longer experimental.
  - version: v12.0.0
    pr-url: https://github.com/nodejs/node/pull/27312
    description: changed from `--diagnostic-report-uncaught-exception` to
                 `--report-uncaught-exception`.
-->

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`

<!-- YAML
added: 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.

Only CommonJS modules are supported.
Use [`--import`][] to preload an [ECMAScript module][].
Modules preloaded with `--require` will run before modules preloaded with `--import`.

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

<!-- YAML
added: 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.

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

<!-- YAML
added: 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.

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

<!-- YAML
added: 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`

<!-- YAML
added:
  - v18.1.0
  - v16.17.0
changes:
  - version: v20.0.0
    pr-url: https://github.com/nodejs/node/pull/46983
    description: The test runner is now stable.
  - version:
      - v19.2.0
      - v18.13.0
    pr-url: https://github.com/nodejs/node/pull/45214
    description: Test runner now supports running in watch mode.
-->

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`

<!-- YAML
added:
  - v21.0.0
  - v20.10.0
  - v18.19.0
-->

The maximum number of test files that the test runner CLI will execute
concurrently. The default value is `os.availableParallelism() - 1`.

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

<!-- YAML
added: v18.11.0
changes:
  - version: v20.0.0
    pr-url: https://github.com/nodejs/node/pull/46983
    description: The test runner is now stable.
-->

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.

### `--test-only`

<!-- YAML
added:
  - v18.0.0
  - v16.17.0
changes:
  - version: v20.0.0
    pr-url: https://github.com/nodejs/node/pull/46983
    description: The test runner is now stable.
-->

Configures the test runner to only execute top level tests that have the `only`
option set.

### `--test-reporter`

<!-- YAML
added:
  - v19.6.0
  - v18.15.0
changes:
  - version: v20.0.0
    pr-url: https://github.com/nodejs/node/pull/46983
    description: The test runner is now stable.
-->

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

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

<!-- YAML
added:
  - v19.6.0
  - v18.15.0
changes:
  - version: v20.0.0
    pr-url: https://github.com/nodejs/node/pull/46983
    description: The test runner is now stable.
-->

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

### `--test-shard`

<!-- YAML
added:
  - 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:

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

### `--test-timeout`

<!-- YAML
added: v21.2.0
-->

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

### `--throw-deprecation`

<!-- YAML
added: v0.11.14
-->

Throw errors for deprecations.

### `--title=title`

<!-- YAML
added: v10.7.0
-->

Set `process.title` on startup.

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

<!-- YAML
added: v4.0.0
-->

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

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

<!-- YAML
added:
 - 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`

<!-- YAML
added:
 - 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`

<!-- YAML
added: v12.0.0
-->

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

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

<!-- YAML
added:
 - 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`

<!-- YAML
added:
 - 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`

<!-- YAML
added:
 - 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`

<!-- YAML
added: 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-atomics-wait`

<!-- YAML
added: v14.3.0
deprecated:
  - v18.8.0
  - v16.18.0
-->

> Stability: 0 - Deprecated

Print short summaries of calls to [`Atomics.wait()`][] to stderr.
The output could look like this:

```text
(node:15701) [Thread 0] Atomics.wait(&lt;address> + 0, 1, inf) started
(node:15701) [Thread 0] Atomics.wait(&lt;address> + 0, 1, inf) did not wait because the values mismatched
(node:15701) [Thread 0] Atomics.wait(&lt;address> + 0, 0, 10) started
(node:15701) [Thread 0] Atomics.wait(&lt;address> + 0, 0, 10) timed out
(node:15701) [Thread 0] Atomics.wait(&lt;address> + 4, 0, inf) started
(node:15701) [Thread 1] Atomics.wait(&lt;address> + 4, -1, inf) started
(node:15701) [Thread 0] Atomics.wait(&lt;address> + 4, 0, inf) was woken up by another thread
(node:15701) [Thread 1] Atomics.wait(&lt;address> + 4, -1, inf) was woken up by another thread
```

The fields here correspond to:

* The thread id as given by [`worker_threads.threadId`][]
* The base address of the `SharedArrayBuffer` in question, as well as the
  byte offset corresponding to the index passed to `Atomics.wait()`
* The expected value that was passed to `Atomics.wait()`
* The timeout passed to `Atomics.wait`

### `--trace-deprecation`

<!-- YAML
added: v0.8.0
-->

Print stack traces for deprecations.

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

<!-- YAML
added: 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`

<!-- YAML
added: v9.8.0
-->

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

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

<!-- YAML
added: v7.7.0
-->

Enables the collection of trace event tracing information.

### `--trace-exit`

<!-- YAML
added:
 - v13.5.0
 - v12.16.0
-->

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

### `--trace-sigint`

<!-- YAML
added:
 - v13.9.0
 - v12.17.0
-->

Prints a stack trace on SIGINT.

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

<!-- YAML
added: v2.1.0
-->

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

### `--trace-tls`

<!-- YAML
added: v12.2.0
-->

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

### `--trace-uncaught`

<!-- YAML
added: 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`

<!-- YAML
added: v6.0.0
-->

Print stack traces for process warnings (including deprecations).

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

<!-- YAML
added: v2.4.0
-->

Track heap object allocations for heap snapshots.

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

<!-- YAML
added:
  - v12.0.0
  - v10.17.0
changes:
  - version: v15.0.0
    pr-url: https://github.com/nodejs/node/pull/33021
    description: Changed default mode to `throw`. Previously, a warning was
                 emitted.
-->

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`

<!-- YAML
added: 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-largepages=mode`

<!-- YAML
added:
 - 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.

### `--v8-options`

<!-- YAML
added: v0.1.3
-->

Print V8 command-line options.

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

<!-- YAML
added: 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`

<!-- YAML
added: v0.1.3
-->

Print node's version.

### `--watch`

<!-- YAML
added:
  - v18.11.0
  - v16.19.0
changes:
  - version:
      - v19.2.0
      - v18.13.0
    pr-url: https://github.com/nodejs/node/pull/45214
    description: Test runner now supports running in watch mode.
-->

> Stability: 1 - Experimental

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.

```bash
node --watch index.js
```

### `--watch-path`

<!-- YAML
added:
  - v18.11.0
  - v16.19.0
-->

> Stability: 1 - Experimental

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.

```bash
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`

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

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

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

<!-- YAML
added: v6.0.0
-->

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

## Environment variables

### `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.

### `NO_COLOR=<any>`

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

### `NODE_DEBUG=module[,…]`

<!-- YAML
added: 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`

<!-- YAML
added: v0.3.0
-->

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

### `NODE_EXTRA_CA_CERTS=file`

<!-- YAML
added: 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()`][emit_warning] 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`

<!-- YAML
added: 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`

<!-- YAML
added: v6.11.0
-->

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

### `NODE_OPTIONS=options...`

<!-- YAML
added: 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:

```bash
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`:

```bash
# 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:

```bash
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:

<!-- node-options-node start -->

* `--allow-addons`
* `--allow-child-process`
* `--allow-fs-read`
* `--allow-fs-write`
* `--allow-worker`
* `--conditions`, `-C`
* `--diagnostic-dir`
* `--disable-proto`
* `--disable-warning`
* `--dns-result-order`
* `--enable-fips`
* `--enable-network-family-autoselection`
* `--enable-source-maps`
* `--experimental-abortcontroller`
* `--experimental-default-type`
* `--experimental-detect-module`
* `--experimental-import-meta-resolve`
* `--experimental-json-modules`
* `--experimental-loader`
* `--experimental-modules`
* `--experimental-network-imports`
* `--experimental-permission`
* `--experimental-policy`
* `--experimental-shadow-realm`
* `--experimental-specifier-resolution`
* `--experimental-top-level-await`
* `--experimental-vm-modules`
* `--experimental-wasi-unstable-preview1`
* `--experimental-wasm-modules`
* `--experimental-websocket`
* `--force-context-aware`
* `--force-fips`
* `--force-node-api-uncaught-exceptions-policy`
* `--frozen-intrinsics`
* `--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`
* `--max-http-header-size`
* `--napi-modules`
* `--no-addons`
* `--no-deprecation`
* `--no-experimental-fetch`
* `--no-experimental-global-customevent`
* `--no-experimental-global-navigator`
* `--no-experimental-global-webcrypto`
* `--no-experimental-repl-await`
* `--no-extra-info-on-fatal-exception`
* `--no-force-async-hooks-checks`
* `--no-global-search-paths`
* `--no-network-family-autoselection`
* `--no-warnings`
* `--node-memory-debug`
* `--openssl-config`
* `--openssl-legacy-provider`
* `--openssl-shared-config`
* `--pending-deprecation`
* `--policy-integrity`
* `--preserve-symlinks-main`
* `--preserve-symlinks`
* `--prof-process`
* `--redirect-warnings`
* `--report-compact`
* `--report-dir`, `--report-directory`
* `--report-filename`
* `--report-on-fatalerror`
* `--report-on-signal`
* `--report-signal`
* `--report-uncaught-exception`
* `--require`, `-r`
* `--secure-heap-min`
* `--secure-heap`
* `--snapshot-blob`
* `--test-only`
* `--test-reporter-destination`
* `--test-reporter`
* `--test-shard`
* `--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-atomics-wait`
* `--trace-deprecation`
* `--trace-event-categories`
* `--trace-event-file-pattern`
* `--trace-events-enabled`
* `--trace-exit`
* `--trace-sigint`
* `--trace-sync-io`
* `--trace-tls`
* `--trace-uncaught`
* `--trace-warnings`
* `--track-heap-objects`
* `--unhandled-rejections`
* `--use-bundled-ca`
* `--use-largepages`
* `--use-openssl-ca`
* `--v8-pool-size`
* `--watch-path`
* `--watch-preserve-output`
* `--watch`
* `--zero-fill-buffers`

<!-- node-options-node end -->

V8 options that are allowed are:

<!-- node-options-v8 start -->

* `--abort-on-uncaught-exception`
* `--disallow-code-generation-from-strings`
* `--enable-etw-stack-walking`
* `--huge-max-old-generation-size`
* `--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`

<!-- node-options-v8 end -->

`--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[:…]`

<!-- YAML
added: 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`

<!-- YAML
added: 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`

<!-- YAML
added: v7.1.0
-->

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

### `NODE_REDIRECT_WARNINGS=file`

<!-- YAML
added: 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`

<!-- YAML
added:
 - 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`

<!-- YAML
added: 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`

<!-- YAML
added: 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_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`:

```json
{
  "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`).

```json
{
  "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
      ]
    }
  }
}
```

### `OPENSSL_CONF=file`

<!-- YAML
added: 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`

<!-- YAML
added: v7.7.0
-->

If `--use-openssl-ca` is enabled, 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`

<!-- YAML
added: v7.7.0
-->

If `--use-openssl-ca` is enabled, 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`

<!-- YAML
added: v0.0.1
changes:
  - version:
     - v16.2.0
    pr-url: https://github.com/nodejs/node/pull/38642
    description:
      Changing the TZ variable using process.env.TZ = changes the timezone
      on Windows as well.
  - version:
     - v13.0.0
    pr-url: https://github.com/nodejs/node/pull/20026
    description:
      Changing the TZ variable using process.env.TZ = changes the timezone
      on POSIX systems.
-->

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.

```console
$ 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). 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:

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

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.

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

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

Sets the maximum [semi-space][] size for V8's [scavenge garbage collector][] in
MiB (megabytes).
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 is 16 MiB for 64-bit systems and 8 MiB for 32-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:

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

[#42511]: https://github.com/nodejs/node/issues/42511
[Chrome DevTools Protocol]: https://chromedevtools.github.io/devtools-protocol/
[CommonJS]: modules.md
[CommonJS module]: modules.md
[CustomEvent Web API]: https://dom.spec.whatwg.org/#customevent
[DEP0025 warning]: deprecations.md#dep0025-requirenodesys
[ECMAScript module]: esm.md#modules-ecmascript-modules
[ExperimentalWarning: `vm.measureMemory` is an experimental feature]: vm.md#vmmeasurememoryoptions
[Fetch API]: https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API
[File System Permissions]: permissions.md#file-system-permissions
[Module customization hooks]: module.md#customization-hooks
[Module customization hooks: enabling]: module.md#enabling
[Modules loaders]: packages.md#modules-loaders
[Navigator API]: globals.md#navigator
[Node.js issue tracker]: https://github.com/nodejs/node/issues
[OSSL_PROVIDER-legacy]: https://www.openssl.org/docs/man3.0/man7/OSSL_PROVIDER-legacy.html
[Permission Model]: permissions.md#permission-model
[REPL]: repl.md
[ScriptCoverage]: https://chromedevtools.github.io/devtools-protocol/tot/Profiler#type-ScriptCoverage
[ShadowRealm]: https://github.com/tc39/proposal-shadowrealm
[Source Map]: https://sourcemaps.info/spec.html
[Subresource Integrity]: https://developer.mozilla.org/en-US/docs/Web/Security/Subresource_Integrity
[V8 JavaScript code coverage]: https://v8project.blogspot.com/2017/12/javascript-code-coverage.html
[Web Crypto API]: webcrypto.md
[`"type"`]: packages.md#type
[`--allow-child-process`]: #--allow-child-process
[`--allow-fs-read`]: #--allow-fs-read
[`--allow-fs-write`]: #--allow-fs-write
[`--allow-worker`]: #--allow-worker
[`--build-snapshot`]: #--build-snapshot
[`--cpu-prof-dir`]: #--cpu-prof-dir
[`--diagnostic-dir`]: #--diagnostic-dirdirectory
[`--experimental-default-type=module`]: #--experimental-default-typetype
[`--experimental-sea-config`]: single-executable-applications.md#generating-single-executable-preparation-blobs
[`--experimental-wasm-modules`]: #--experimental-wasm-modules
[`--heap-prof-dir`]: #--heap-prof-dir
[`--import`]: #--importmodule
[`--openssl-config`]: #--openssl-configfile
[`--preserve-symlinks`]: #--preserve-symlinks
[`--print`]: #-p---print-script
[`--redirect-warnings`]: #--redirect-warningsfile
[`--require`]: #-r---require-module
[`Atomics.wait()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Atomics/wait
[`Buffer`]: buffer.md#class-buffer
[`CRYPTO_secure_malloc_init`]: https://www.openssl.org/docs/man3.0/man3/CRYPTO_secure_malloc_init.html
[`NODE_OPTIONS`]: #node_optionsoptions
[`NO_COLOR`]: https://no-color.org
[`SlowBuffer`]: buffer.md#class-slowbuffer
[`WebSocket`]: https://developer.mozilla.org/en-US/docs/Web/API/WebSocket
[`YoungGenerationSizeFromSemiSpaceSize`]: https://chromium.googlesource.com/v8/v8.git/+/refs/tags/10.3.129/src/heap/heap.cc#328
[`dns.lookup()`]: dns.md#dnslookuphostname-options-callback
[`dns.setDefaultResultOrder()`]: dns.md#dnssetdefaultresultorderorder
[`dnsPromises.lookup()`]: dns.md#dnspromiseslookuphostname-options
[`import` specifier]: esm.md#import-specifiers
[`process.setUncaughtExceptionCaptureCallback()`]: process.md#processsetuncaughtexceptioncapturecallbackfn
[`tls.DEFAULT_MAX_VERSION`]: tls.md#tlsdefault_max_version
[`tls.DEFAULT_MIN_VERSION`]: tls.md#tlsdefault_min_version
[`unhandledRejection`]: process.md#event-unhandledrejection
[`v8.startupSnapshot` API]: v8.md#startup-snapshot-api
[`worker_threads.threadId`]: worker_threads.md#workerthreadid
[collecting code coverage from tests]: test.md#collecting-code-coverage
[conditional exports]: packages.md#conditional-exports
[context-aware]: addons.md#context-aware-addons
[debugger]: debugger.md
[debugging security implications]: https://nodejs.org/en/docs/guides/debugging-getting-started/#security-implications
[deprecation warnings]: deprecations.md#list-of-deprecated-apis
[emit_warning]: process.md#processemitwarningwarning-options
[environment_variables]: #environment-variables
[filtering tests by name]: test.md#filtering-tests-by-name
[jitless]: https://v8.dev/blog/jitless
[libuv threadpool documentation]: https://docs.libuv.org/en/latest/threadpool.html
[remote code execution]: https://www.owasp.org/index.php/Code_Injection
[running tests from the command line]: test.md#running-tests-from-the-command-line
[scavenge garbage collector]: https://v8.dev/blog/orinoco-parallel-scavenger
[security warning]: #warning-binding-inspector-to-a-public-ipport-combination-is-insecure
[semi-space]: https://www.memorymanagement.org/glossary/s.html#semi.space
[single executable application]: single-executable-applications.md
[test reporters]: test.md#test-reporters
[timezone IDs]: https://en.wikipedia.org/wiki/List_of_tz_database_time_zones
[tracking issue for user-land snapshots]: https://github.com/nodejs/node/issues/44014
[ways that `TZ` is handled in other environments]: https://www.gnu.org/software/libc/manual/html_node/TZ-Variable.html