Command-line API | Node.js v23.11.0 Documentation (original) (raw)

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. If no corresponding file is found, an error is thrown.

If a file is found, its path will be passed to theES module loader under any of the following conditions:

Otherwise, the file is loaded using the CommonJS module loader. SeeModules loaders for more details.

ECMAScript modules loader entry point caveat#

When loading, the ES module loader loads the program entry point, the node command will accept as input only files with .js,.mjs, or .cjs extensions. With the following flags, additional file extensions are enabled:

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_OPTIONSenvironment 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 throughprocess.setUncaughtExceptionCaptureCallback() (and through usage of thenode:domain module that uses it).

--allow-addons#

Added in: v21.6.0, v20.12.0

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. (/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#

Added in: v20.0.0

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' }

Unlike child_process.spawn, the child_process.fork API copies the execution arguments from the parent process. This means that if you start Node.js with the Permission Model enabled and include the --allow-child-process flag, callingchild_process.fork() will propagate all Permission Model flags to the child process.

--allow-fs-read#

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

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

Examples can be found in the File System Permissions documentation.

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

`$ node --permission index.js

Error: Access to this API has been restricted at node:internal/main/run_main_module:23:47 { code: 'ERR_ACCESS_DENIED', permission: 'FileSystemRead', resource: '/Users/rafaelgss/repos/os/node/index.js' }`

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

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

--allow-fs-write#

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

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

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-wasi#

Added in: v22.3.0, v20.16.0

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

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#

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.blobin 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.

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 thetracking issue for user-land snapshots.

--build-snapshot-config#

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:

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#

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#

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#

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 will be used as-is; patterns such as${hhmmss} or ${pid} are not supported.

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

--cpu-prof-dir#

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#

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

--cpu-prof-name#

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:

--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#

Added in: v23.7.0

Disable the ability of starting a debugging session by sending aSIGUSR1 signal to the process.

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

Added in: v21.3.0, v20.11.0

Disable specific process warnings by code or type.

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

List of deprecation warnings.

The Node.js core warning types are: DeprecationWarning andExperimentalWarning

For example, the following script will not emitDEP0025 require('node:sys') when executed withnode --disable-warning=DEP0025:

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

For example, the following script will emit theDEP0025 require('node:sys'), but not any Experimental Warnings (such asExperimentalWarning: vm.measureMemory is an experimental featurein <=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.jsnode:vm module.

--dns-result-order=order#

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

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#

Enable Source Map v3 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 originalError.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

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=config#

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=config#

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"#

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-experimental-strip-types flag is provided.

--experimental-addon-modules#

Added in: v23.6.0

Enable experimental import support for .node addons.

--experimental-async-context-frame#

Added in: v22.7.0

Enables the use of AsyncLocalStorage backed by AsyncContextFrame rather than the default implementation which relies on async_hooks. This new model is implemented very differently and so could have differences in how context data flows within the application. As such, it is presently recommended to be sure your application behaviour is unaffected by this change before using it in production.

--experimental-config-file=config#

Added in: v23.10.0

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.Zin 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 } }

In the nodeOptions field, only flags that are allowed in NODE_OPTIONS are supported. No-op flags are not supported. Not all V8 flags are currently supported.

It is possible to use the official JSON schemato 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

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_OPTIONSenv file parsed by the --env-file flag.

If duplicate keys are present in the configuration file, only the first key will be used.

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

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

If the --experimental-default-config-file flag is present, Node.js will look for anode.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#

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-network-inspection#

Added in: v22.6.0, v20.18.0

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-shadow-realm#

Added in: v19.0.0, v18.13.0

Use this flag to enable ShadowRealm support.

--experimental-test-coverage#

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 oncollecting code coverage from tests for more details.

--experimental-test-module-mocks#

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

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#

Enable experimental WebAssembly System Interface (WASI) support.

--experimental-wasm-modules#

Added in: v12.3.0

Enable experimental WebAssembly module support.

--experimental-webstorage#

Added in: v22.4.0

Enable experimental Web Storage support.

--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

Enable experimental frozen intrinsics like Array and Object.

Only the root context is supported. There is no guarantee thatglobalThis.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#

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#

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#

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

--heap-prof-name#

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

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

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

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#

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-experimental-strip-types. The default is "commonjs".

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_SYNTAXor 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:

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

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:

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]#

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.

--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 hostparameter 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/listendpoint 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.

--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.

-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

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. This flag is a no-op unless Node.js is started with the --experimental-webstorage flag.

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

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

--napi-modules#

Added in: v7.10.0

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

--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-deprecation#

Added in: v0.8.0

Silence deprecation warnings.

--no-experimental-detect-module#

Disable using syntax detection to determine module type.

--no-experimental-global-navigator#

Added in: v21.2.0

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-sqlite#

Disable the experimental node:sqlite module.

--no-experimental-strip-types#

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

--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#

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

--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 seeOSSL_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 namedopenssl.cnf but this can be changed using the environment variableOPENSSL_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 theNODE_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#

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

--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 allowsnode --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"#

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#

Location at which the report will be generated.

--report-exclude-env#

Added in: v23.3.0

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#

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#

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#

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#

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

--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#

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#

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.jsonfile 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, ifancestor-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 runcommands 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:

Environment variables#

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

--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

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#

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 linefor 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 toos.availableParallelism() - 1.

--test-coverage-branches=threshold#

Added in: v22.8.0

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

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

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

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

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-isolation=mode#

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#

A regular expression that configures the test runner to only execute tests whose name matches the provided pattern. See the documentation onfiltering 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#

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

--test-reporter#

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

--test-reporter-destination#

The destination for the corresponding test reporter. See the documentation ontest reporters 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 partstotal 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 onfiltering 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#

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 SSLKEYLOGFILEformat 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

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

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

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

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

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#

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

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-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:

--use-system-ca#

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 planned to followChromium's policy for locally trusted certificates:

On macOS, the following settings are respected:

On Windows, the following settings are respected (unlike Chromium's policy, distrust and intermediate CA are not currently supported):

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

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#

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.

node --watch index.js

--watch-path#

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.

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 SlowBufferinstances.

Environment variables#

FORCE_COLOR=[1, 2, 3]#

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

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_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_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) withprocess.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 caoptions 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 usingprocess.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 itsNODE_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.

V8 options that are allowed are:

--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 theNODE_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#

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_V8_COVERAGE=dir#

When set, Node.js will begin outputting V8 JavaScript code coverage andSource 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#

If found, source map data is appended to the top-level key source-map-cacheon 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#

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:

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 nodewill 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#

--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 (seeYoungGenerationSizeFromSemiSpaceSize 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