Node.js v19.9.0 documentation

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 the ECMAScript module loader 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.
• 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 ECMAScript module loader loads the program entry point, the node command will only accept as input only files with .js, .mjs, or .cjs extensions; and with .wasm extensions when --experimental-wasm-modules is 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_OPTIONS environment variable.

-#

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.

--#

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#

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).

--build-snapshot#

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

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

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

# Run snapshot.js to intialize 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 copy

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 copy

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.

--completion-bash#

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

$ node --completion-bash > node_bash_completion
$ source node_bash_completion copy

-C condition, --conditions=condition#

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:

$ node -C development app.js copy

--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 copy

--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:

• --cpu-prof-dir
• --heap-prof-dir
• --redirect-warnings

--disable-proto=mode#

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#

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#

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#

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

--enable-network-family-autoselection#

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 prevents --enable-source-maps from modifying the stack 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.

--experimental-import-meta-resolve#

Enable experimental import.meta.resolve() support.

--experimental-loader=module#

Specify the module of a custom experimental ECMAScript module loader. module may be any string accepted as an import specifier.

--experimental-network-imports#

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

--experimental-policy#

Use the specified file as a security policy.

--no-experimental-fetch#

Disable experimental support for the Fetch API.

--no-experimental-global-webcrypto#

Disable exposition of Web Crypto API on the global scope.

--no-experimental-global-customevent#

Disable exposition of CustomEvent Web API on the global scope.

--no-experimental-repl-await#

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

--experimental-shadow-realm#

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 on collecting code coverage from tests for more details.

--experimental-vm-modules#

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

--experimental-wasi-unstable-preview1#

Enable experimental WebAssembly System Interface (WASI) support.

--experimental-wasm-modules#

Enable experimental WebAssembly module support.

--force-context-aware#

Disable loading native addons that are not context-aware.

--force-fips#

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

--frozen-intrinsics#

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.

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

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.

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

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
.... copy

--heapsnapshot-signal=signal#

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 copy

--heap-prof#