The process object provides information about, and control over, the current
Node.js process. While it is available as a global, it is recommended to
explicitly access it via require or import:
import process from 'process';const process = require('process');The process object is an instance of EventEmitter.
The 'beforeExit' event is emitted when Node.js empties its event loop and has
no additional work to schedule. Normally, the Node.js process will exit when
there is no work scheduled, but a listener registered on the 'beforeExit'
event can make asynchronous calls, and thereby cause the Node.js process to
continue.
The listener callback function is invoked with the value of
process.exitCode passed as the only argument.
The 'beforeExit' event is not emitted for conditions causing explicit
termination, such as calling process.exit() or uncaught exceptions.
The 'beforeExit' should not be used as an alternative to the 'exit' event
unless the intention is to schedule additional work.
import process from 'process';
process.on('beforeExit', (code) => {
console.log('Process beforeExit event with code: ', code);
});
process.on('exit', (code) => {
console.log('Process exit event with code: ', code);
});
console.log('This message is displayed first.');
// Prints:
// This message is displayed first.
// Process beforeExit event with code: 0
// Process exit event with code: 0const process = require('process');
process.on('beforeExit', (code) => {
console.log('Process beforeExit event with code: ', code);
});
process.on('exit', (code) => {
console.log('Process exit event with code: ', code);
});
console.log('This message is displayed first.');
// Prints:
// This message is displayed first.
// Process beforeExit event with code: 0
// Process exit event with code: 0If the Node.js process is spawned with an IPC channel (see the Child Process
and Cluster documentation), the 'disconnect' event will be emitted when
the IPC channel is closed.
code{integer}
The 'exit' event is emitted when the Node.js process is about to exit as a
result of either:
- The
process.exit()method being called explicitly; - The Node.js event loop no longer having any additional work to perform.
There is no way to prevent the exiting of the event loop at this point, and once
all 'exit' listeners have finished running the Node.js process will terminate.
The listener callback function is invoked with the exit code specified either
by the process.exitCode property, or the exitCode argument passed to the
process.exit() method.
import process from 'process';
process.on('exit', (code) => {
console.log(`About to exit with code: ${code}`);
});const process = require('process');
process.on('exit', (code) => {
console.log(`About to exit with code: ${code}`);
});Listener functions must only perform synchronous operations. The Node.js
process will exit immediately after calling the 'exit' event listeners
causing any additional work still queued in the event loop to be abandoned.
In the following example, for instance, the timeout will never occur:
import process from 'process';
process.on('exit', (code) => {
setTimeout(() => {
console.log('This will not run');
}, 0);
});const process = require('process');
process.on('exit', (code) => {
setTimeout(() => {
console.log('This will not run');
}, 0);
});message{ Object | boolean | number | string | null } a parsed JSON object or a serializable primitive value.sendHandle{net.Server|net.Socket} anet.Serverornet.Socketobject, or undefined.
If the Node.js process is spawned with an IPC channel (see the Child Process
and Cluster documentation), the 'message' event is emitted whenever a
message sent by a parent process using childprocess.send() is received by
the child process.
The message goes through serialization and parsing. The resulting message might not be the same as what is originally sent.
If the serialization option was set to advanced used when spawning the
process, the message argument can contain data that JSON is not able
to represent.
See Advanced serialization for child_process for more details.
Stability: 0 - Deprecated
type{string} The resolution type. One of'resolve'or'reject'.promise{Promise} The promise that resolved or rejected more than once.value{any} The value with which the promise was either resolved or rejected after the original resolve.
The 'multipleResolves' event is emitted whenever a Promise has been either:
- Resolved more than once.
- Rejected more than once.
- Rejected after resolve.
- Resolved after reject.
This is useful for tracking potential errors in an application while using the
Promise constructor, as multiple resolutions are silently swallowed. However,
the occurrence of this event does not necessarily indicate an error. For
example, Promise.race() can trigger a 'multipleResolves' event.
Because of the unreliability of the event in cases like the
Promise.race() example above it has been deprecated.
import process from 'process';
process.on('multipleResolves', (type, promise, reason) => {
console.error(type, promise, reason);
setImmediate(() => process.exit(1));
});
async function main() {
try {
return await new Promise((resolve, reject) => {
resolve('First call');
resolve('Swallowed resolve');
reject(new Error('Swallowed reject'));
});
} catch {
throw new Error('Failed');
}
}
main().then(console.log);
// resolve: Promise { 'First call' } 'Swallowed resolve'
// reject: Promise { 'First call' } Error: Swallowed reject
// at Promise (*)
// at new Promise (<anonymous>)
// at main (*)
// First callconst process = require('process');
process.on('multipleResolves', (type, promise, reason) => {
console.error(type, promise, reason);
setImmediate(() => process.exit(1));
});
async function main() {
try {
return await new Promise((resolve, reject) => {
resolve('First call');
resolve('Swallowed resolve');
reject(new Error('Swallowed reject'));
});
} catch {
throw new Error('Failed');
}
}
main().then(console.log);
// resolve: Promise { 'First call' } 'Swallowed resolve'
// reject: Promise { 'First call' } Error: Swallowed reject
// at Promise (*)
// at new Promise (<anonymous>)
// at main (*)
// First callpromise{Promise} The late handled promise.
The 'rejectionHandled' event is emitted whenever a Promise has been rejected
and an error handler was attached to it (using promise.catch(), for
example) later than one turn of the Node.js event loop.
The Promise object would have previously been emitted in an
'unhandledRejection' event, but during the course of processing gained a
rejection handler.
There is no notion of a top level for a Promise chain at which rejections can
always be handled. Being inherently asynchronous in nature, a Promise
rejection can be handled at a future point in time, possibly much later than
the event loop turn it takes for the 'unhandledRejection' event to be emitted.
Another way of stating this is that, unlike in synchronous code where there is an ever-growing list of unhandled exceptions, with Promises there can be a growing-and-shrinking list of unhandled rejections.
In synchronous code, the 'uncaughtException' event is emitted when the list of
unhandled exceptions grows.
In asynchronous code, the 'unhandledRejection' event is emitted when the list
of unhandled rejections grows, and the 'rejectionHandled' event is emitted
when the list of unhandled rejections shrinks.
import process from 'process';
const unhandledRejections = new Map();
process.on('unhandledRejection', (reason, promise) => {
unhandledRejections.set(promise, reason);
});
process.on('rejectionHandled', (promise) => {
unhandledRejections.delete(promise);
});const process = require('process');
const unhandledRejections = new Map();
process.on('unhandledRejection', (reason, promise) => {
unhandledRejections.set(promise, reason);
});
process.on('rejectionHandled', (promise) => {
unhandledRejections.delete(promise);
});In this example, the unhandledRejections Map will grow and shrink over time,
reflecting rejections that start unhandled and then become handled. It is
possible to record such errors in an error log, either periodically (which is
likely best for long-running application) or upon process exit (which is likely
most convenient for scripts).
err{Error} The uncaught exception.origin{string} Indicates if the exception originates from an unhandled rejection or from a synchronous error. Can either be'uncaughtException'or'unhandledRejection'. The latter is used when in an exception happens in aPromisebased async context (or if aPromiseis rejected) and--unhandled-rejectionsflag set tostrictorthrow(which is the default) and the rejection is not handled, or when a rejection happens during the command line entry point's ES module static loading phase.
The 'uncaughtException' event is emitted when an uncaught JavaScript
exception bubbles all the way back to the event loop. By default, Node.js
handles such exceptions by printing the stack trace to stderr and exiting
with code 1, overriding any previously set process.exitCode.
Adding a handler for the 'uncaughtException' event overrides this default
behavior. Alternatively, change the process.exitCode in the
'uncaughtException' handler which will result in the process exiting with the
provided exit code. Otherwise, in the presence of such handler the process will
exit with 0.
import process from 'process';
process.on('uncaughtException', (err, origin) => {
fs.writeSync(
process.stderr.fd,
`Caught exception: ${err}\n` +
`Exception origin: ${origin}`
);
});
setTimeout(() => {
console.log('This will still run.');
}, 500);
// Intentionally cause an exception, but don't catch it.
nonexistentFunc();
console.log('This will not run.');const process = require('process');
process.on('uncaughtException', (err, origin) => {
fs.writeSync(
process.stderr.fd,
`Caught exception: ${err}\n` +
`Exception origin: ${origin}`
);
});
setTimeout(() => {
console.log('This will still run.');
}, 500);
// Intentionally cause an exception, but don't catch it.
nonexistentFunc();
console.log('This will not run.');It is possible to monitor 'uncaughtException' events without overriding the
default behavior to exit the process by installing a
'uncaughtExceptionMonitor' listener.
'uncaughtException' is a crude mechanism for exception handling
intended to be used only as a last resort. The event should not be used as
an equivalent to On Error Resume Next. Unhandled exceptions inherently mean
that an application is in an undefined state. Attempting to resume application
code without properly recovering from the exception can cause additional
unforeseen and unpredictable issues.
Exceptions thrown from within the event handler will not be caught. Instead the process will exit with a non-zero exit code and the stack trace will be printed. This is to avoid infinite recursion.
Attempting to resume normally after an uncaught exception can be similar to pulling out the power cord when upgrading a computer. Nine out of ten times, nothing happens. But the tenth time, the system becomes corrupted.
The correct use of 'uncaughtException' is to perform synchronous cleanup
of allocated resources (e.g. file descriptors, handles, etc) before shutting
down the process. It is not safe to resume normal operation after
'uncaughtException'.
To restart a crashed application in a more reliable way, whether
'uncaughtException' is emitted or not, an external monitor should be employed
in a separate process to detect application failures and recover or restart as
needed.
err{Error} The uncaught exception.origin{string} Indicates if the exception originates from an unhandled rejection or from synchronous errors. Can either be'uncaughtException'or'unhandledRejection'. The latter is used when in an exception happens in aPromisebased async context (or if aPromiseis rejected) and--unhandled-rejectionsflag set tostrictorthrow(which is the default) and the rejection is not handled, or when a rejection happens during the command line entry point's ES module static loading phase.
The 'uncaughtExceptionMonitor' event is emitted before an
'uncaughtException' event is emitted or a hook installed via
process.setUncaughtExceptionCaptureCallback() is called.
Installing an 'uncaughtExceptionMonitor' listener does not change the behavior
once an 'uncaughtException' event is emitted. The process will
still crash if no 'uncaughtException' listener is installed.
import process from 'process';
process.on('uncaughtExceptionMonitor', (err, origin) => {
MyMonitoringTool.logSync(err, origin);
});
// Intentionally cause an exception, but don't catch it.
nonexistentFunc();
// Still crashes Node.jsconst process = require('process');
process.on('uncaughtExceptionMonitor', (err, origin) => {
MyMonitoringTool.logSync(err, origin);
});
// Intentionally cause an exception, but don't catch it.
nonexistentFunc();
// Still crashes Node.jsreason{Error|any} The object with which the promise was rejected (typically anErrorobject).promise{Promise} The rejected promise.
The 'unhandledRejection' event is emitted whenever a Promise is rejected and
no error handler is attached to the promise within a turn of the event loop.
When programming with Promises, exceptions are encapsulated as "rejected
promises". Rejections can be caught and handled using promise.catch() and
are propagated through a Promise chain. The 'unhandledRejection' event is
useful for detecting and keeping track of promises that were rejected whose
rejections have not yet been handled.
import process from 'process';
process.on('unhandledRejection', (reason, promise) => {
console.log('Unhandled Rejection at:', promise, 'reason:', reason);
// Application specific logging, throwing an error, or other logic here
});
somePromise.then((res) => {
return reportToUser(JSON.pasre(res)); // Note the typo (`pasre`)
}); // No `.catch()` or `.then()`const process = require('process');
process.on('unhandledRejection', (reason, promise) => {
console.log('Unhandled Rejection at:', promise, 'reason:', reason);
// Application specific logging, throwing an error, or other logic here
});
somePromise.then((res) => {
return reportToUser(JSON.pasre(res)); // Note the typo (`pasre`)
}); // No `.catch()` or `.then()`The following will also trigger the 'unhandledRejection' event to be
emitted:
import process from 'process';
function SomeResource() {
// Initially set the loaded status to a rejected promise
this.loaded = Promise.reject(new Error('Resource not yet loaded!'));
}
const resource = new SomeResource();
// no .catch or .then on resource.loaded for at least a turnconst process = require('process');
function SomeResource() {
// Initially set the loaded status to a rejected promise
this.loaded = Promise.reject(new Error('Resource not yet loaded!'));
}
const resource = new SomeResource();
// no .catch or .then on resource.loaded for at least a turnIn this example case, it is possible to track the rejection as a developer error
as would typically be the case for other 'unhandledRejection' events. To
address such failures, a non-operational
.catch(() => { }) handler may be attached to
resource.loaded, which would prevent the 'unhandledRejection' event from
being emitted.
warning{Error} Key properties of the warning are:name{string} The name of the warning. Default:'Warning'.message{string} A system-provided description of the warning.stack{string} A stack trace to the location in the code where the warning was issued.
The 'warning' event is emitted whenever Node.js emits a process warning.
A process warning is similar to an error in that it describes exceptional conditions that are being brought to the user's attention. However, warnings are not part of the normal Node.js and JavaScript error handling flow. Node.js can emit warnings whenever it detects bad coding practices that could lead to sub-optimal application performance, bugs, or security vulnerabilities.
import process from 'process';
process.on('warning', (warning) => {
console.warn(warning.name); // Print the warning name
console.warn(warning.message); // Print the warning message
console.warn(warning.stack); // Print the stack trace
});const process = require('process');
process.on('warning', (warning) => {
console.warn(warning.name); // Print the warning name
console.warn(warning.message); // Print the warning message
console.warn(warning.stack); // Print the stack trace
});By default, Node.js will print process warnings to stderr. The --no-warnings
command-line option can be used to suppress the default console output but the
'warning' event will still be emitted by the process object.
The following example illustrates the warning that is printed to stderr when
too many listeners have been added to an event:
$ node
> events.defaultMaxListeners = 1;
> process.on('foo', () => {});
> process.on('foo', () => {});
> (node:38638) MaxListenersExceededWarning: Possible EventEmitter memory leak
detected. 2 foo listeners added. Use emitter.setMaxListeners() to increase limitIn contrast, the following example turns off the default warning output and
adds a custom handler to the 'warning' event:
$ node --no-warnings
> const p = process.on('warning', (warning) => console.warn('Do not do that!'));
> events.defaultMaxListeners = 1;
> process.on('foo', () => {});
> process.on('foo', () => {});
> Do not do that!The --trace-warnings command-line option can be used to have the default
console output for warnings include the full stack trace of the warning.
Launching Node.js using the --throw-deprecation command-line flag will
cause custom deprecation warnings to be thrown as exceptions.
Using the --trace-deprecation command-line flag will cause the custom
deprecation to be printed to stderr along with the stack trace.
Using the --no-deprecation command-line flag will suppress all reporting
of the custom deprecation.
The *-deprecation command-line flags only affect warnings that use the name
'DeprecationWarning'.
worker{Worker} The {Worker} that was created.
The 'worker' event is emitted after a new {Worker} thread has been created.
See the process.emitWarning() method for issuing
custom or application-specific warnings.
There are no strict guidelines for warning types (as identified by the name
property) emitted by Node.js. New types of warnings can be added at any time.
A few of the warning types that are most common include:
'DeprecationWarning'- Indicates use of a deprecated Node.js API or feature. Such warnings must include a'code'property identifying the deprecation code.'ExperimentalWarning'- Indicates use of an experimental Node.js API or feature. Such features must be used with caution as they may change at any time and are not subject to the same strict semantic-versioning and long-term support policies as supported features.'MaxListenersExceededWarning'- Indicates that too many listeners for a given event have been registered on either anEventEmitterorEventTarget. This is often an indication of a memory leak.'TimeoutOverflowWarning'- Indicates that a numeric value that cannot fit within a 32-bit signed integer has been provided to either thesetTimeout()orsetInterval()functions.'UnsupportedWarning'- Indicates use of an unsupported option or feature that will be ignored rather than treated as an error. One example is use of the HTTP response status message when using the HTTP/2 compatibility API.
Signal events will be emitted when the Node.js process receives a signal. Please
refer to signal(7) for a listing of standard POSIX signal names such as
'SIGINT', 'SIGHUP', etc.
Signals are not available on Worker threads.
The signal handler will receive the signal's name ('SIGINT',
'SIGTERM', etc.) as the first argument.
The name of each event will be the uppercase common name for the signal (e.g.
'SIGINT' for SIGINT signals).
import process from 'process';
// Begin reading from stdin so the process does not exit.
process.stdin.resume();
process.on('SIGINT', () => {
console.log('Received SIGINT. Press Control-D to exit.');
});
// Using a single function to handle multiple signals
function handle(signal) {
console.log(`Received ${signal}`);
}
process.on('SIGINT', handle);
process.on('SIGTERM', handle);const process = require('process');
// Begin reading from stdin so the process does not exit.
process.stdin.resume();
process.on('SIGINT', () => {
console.log('Received SIGINT. Press Control-D to exit.');
});
// Using a single function to handle multiple signals
function handle(signal) {
console.log(`Received ${signal}`);
}
process.on('SIGINT', handle);
process.on('SIGTERM', handle);'SIGUSR1'is reserved by Node.js to start the debugger. It's possible to install a listener but doing so might interfere with the debugger.'SIGTERM'and'SIGINT'have default handlers on non-Windows platforms that reset the terminal mode before exiting with code128 + signal number. If one of these signals has a listener installed, its default behavior will be removed (Node.js will no longer exit).'SIGPIPE'is ignored by default. It can have a listener installed.'SIGHUP'is generated on Windows when the console window is closed, and on other platforms under various similar conditions. See signal(7). It can have a listener installed, however Node.js will be unconditionally terminated by Windows about 10 seconds later. On non-Windows platforms, the default behavior ofSIGHUPis to terminate Node.js, but once a listener has been installed its default behavior will be removed.'SIGTERM'is not supported on Windows, it can be listened on.'SIGINT'from the terminal is supported on all platforms, and can usually be generated with Ctrl+C (though this may be configurable). It is not generated when terminal raw mode is enabled and Ctrl+C is used.'SIGBREAK'is delivered on Windows when Ctrl+Break is pressed. On non-Windows platforms, it can be listened on, but there is no way to send or generate it.'SIGWINCH'is delivered when the console has been resized. On Windows, this will only happen on write to the console when the cursor is being moved, or when a readable tty is used in raw mode.'SIGKILL'cannot have a listener installed, it will unconditionally terminate Node.js on all platforms.'SIGSTOP'cannot have a listener installed.'SIGBUS','SIGFPE','SIGSEGV'and'SIGILL', when not raised artificially using kill(2), inherently leave the process in a state from which it is not safe to call JS listeners. Doing so might cause the process to stop responding.0can be sent to test for the existence of a process, it has no effect if the process exists, but will throw an error if the process does not exist.
Windows does not support signals so has no equivalent to termination by signal,
but Node.js offers some emulation with process.kill(), and
subprocess.kill():
- Sending
SIGINT,SIGTERM, andSIGKILLwill cause the unconditional termination of the target process, and afterwards, subprocess will report that the process was terminated by signal. - Sending signal
0can be used as a platform independent way to test for the existence of a process.
The process.abort() method causes the Node.js process to exit immediately and
generate a core file.
This feature is not available in Worker threads.
- {Set}
The process.allowedNodeEnvironmentFlags property is a special,
read-only Set of flags allowable within the NODE_OPTIONS
environment variable.
process.allowedNodeEnvironmentFlags extends Set, but overrides
Set.prototype.has to recognize several different possible flag
representations. process.allowedNodeEnvironmentFlags.has() will
return true in the following cases:
- Flags may omit leading single (
-) or double (--) dashes; e.g.,inspect-brkfor--inspect-brk, orrfor-r. - Flags passed through to V8 (as listed in
--v8-options) may replace one or more non-leading dashes for an underscore, or vice-versa; e.g.,--perf_basic_prof,--perf-basic-prof,--perf_basic-prof, etc. - Flags may contain one or more equals (
=) characters; all characters after and including the first equals will be ignored; e.g.,--stack-trace-limit=100. - Flags must be allowable within
NODE_OPTIONS.
When iterating over process.allowedNodeEnvironmentFlags, flags will
appear only once; each will begin with one or more dashes. Flags
passed through to V8 will contain underscores instead of non-leading
dashes:
import { allowedNodeEnvironmentFlags } from 'process';
allowedNodeEnvironmentFlags.forEach((flag) => {
// -r
// --inspect-brk
// --abort_on_uncaught_exception
// ...
});const { allowedNodeEnvironmentFlags } = require('process');
allowedNodeEnvironmentFlags.forEach((flag) => {
// -r
// --inspect-brk
// --abort_on_uncaught_exception
// ...
});The methods add(), clear(), and delete() of
process.allowedNodeEnvironmentFlags do nothing, and will fail
silently.
If Node.js was compiled without NODE_OPTIONS support (shown in
process.config), process.allowedNodeEnvironmentFlags will
contain what would have been allowable.
- {string}
The operating system CPU architecture for which the Node.js binary was compiled.
Possible values are: 'arm', 'arm64', 'ia32', 'mips','mipsel', 'ppc',
'ppc64', 's390', 's390x', and 'x64'.
import { arch } from 'process';
console.log(`This processor architecture is ${arch}`);const { arch } = require('process');
console.log(`This processor architecture is ${arch}`);- {string[]}
The process.argv property returns an array containing the command-line
arguments passed when the Node.js process was launched. The first element will
be process.execPath. See process.argv0 if access to the original value
of argv[0] is needed. The second element will be the path to the JavaScript
file being executed. The remaining elements will be any additional command-line
arguments.
For example, assuming the following script for process-args.js:
import { argv } from 'process';
// print process.argv
argv.forEach((val, index) => {
console.log(`${index}: ${val}`);
});const { argv } = require('process');
// print process.argv
argv.forEach((val, index) => {
console.log(`${index}: ${val}`);
});Launching the Node.js process as:
$ node process-args.js one two=three fourWould generate the output:
0: /usr/local/bin/node
1: /Users/mjr/work/node/process-args.js
2: one
3: two=three
4: four
- {string}
The process.argv0 property stores a read-only copy of the original value of
argv[0] passed when Node.js starts.
$ bash -c 'exec -a customArgv0 ./node'
> process.argv[0]
'/Volumes/code/external/node/out/Release/node'
> process.argv0
'customArgv0'- {Object}
If the Node.js process was spawned with an IPC channel (see the
Child Process documentation), the process.channel
property is a reference to the IPC channel. If no IPC channel exists, this
property is undefined.
This method makes the IPC channel keep the event loop of the process
running if .unref() has been called before.
Typically, this is managed through the number of 'disconnect' and 'message'
listeners on the process object. However, this method can be used to
explicitly request a specific behavior.
This method makes the IPC channel not keep the event loop of the process running, and lets it finish even while the channel is open.
Typically, this is managed through the number of 'disconnect' and 'message'
listeners on the process object. However, this method can be used to
explicitly request a specific behavior.
directory{string}
The process.chdir() method changes the current working directory of the
Node.js process or throws an exception if doing so fails (for instance, if
the specified directory does not exist).
import { chdir, cwd } from 'process';
console.log(`Starting directory: ${cwd()}`);
try {
chdir('/tmp');
console.log(`New directory: ${cwd()}`);
} catch (err) {
console.error(`chdir: ${err}`);
}const { chdir, cwd } = require('process');
console.log(`Starting directory: ${cwd()}`);
try {
chdir('/tmp');
console.log(`New directory: ${cwd()}`);
} catch (err) {
console.error(`chdir: ${err}`);
}This feature is not available in Worker threads.
- {Object}
The process.config property returns an Object containing the JavaScript
representation of the configure options used to compile the current Node.js
executable. This is the same as the config.gypi file that was produced when
running the ./configure script.
An example of the possible output looks like:
{
target_defaults:
{ cflags: [],
default_configuration: 'Release',
defines: [],
include_dirs: [],
libraries: [] },
variables:
{
host_arch: 'x64',
napi_build_version: 5,
node_install_npm: 'true',
node_prefix: '',
node_shared_cares: 'false',
node_shared_http_parser: 'false',
node_shared_libuv: 'false',
node_shared_zlib: 'false',
node_use_dtrace: 'false',
node_use_openssl: 'true',
node_shared_openssl: 'false',
strict_aliasing: 'true',
target_arch: 'x64',
v8_use_snapshot: 1
}
}The process.config property is not read-only and there are existing
modules in the ecosystem that are known to extend, modify, or entirely replace
the value of process.config.
Modifying the process.config property, or any child-property of the
process.config object has been deprecated. The process.config will be made
read-only in a future release.
- {boolean}
If the Node.js process is spawned with an IPC channel (see the Child Process
and Cluster documentation), the process.connected property will return
true so long as the IPC channel is connected and will return false after
process.disconnect() is called.
Once process.connected is false, it is no longer possible to send messages
over the IPC channel using process.send().
previousValue{Object} A previous return value from callingprocess.cpuUsage()- Returns: {Object}
user{integer}system{integer}
The process.cpuUsage() method returns the user and system CPU time usage of
the current process, in an object with properties user and system, whose
values are microsecond values (millionth of a second). These values measure time
spent in user and system code respectively, and may end up being greater than
actual elapsed time if multiple CPU cores are performing work for this process.
The result of a previous call to process.cpuUsage() can be passed as the
argument to the function, to get a diff reading.
import { cpuUsage } from 'process';
const startUsage = cpuUsage();
// { user: 38579, system: 6986 }
// spin the CPU for 500 milliseconds
const now = Date.now();
while (Date.now() - now < 500);
console.log(cpuUsage(startUsage));
// { user: 514883, system: 11226 }const { cpuUsage } = require('process');
const startUsage = cpuUsage();
// { user: 38579, system: 6986 }
// spin the CPU for 500 milliseconds
const now = Date.now();
while (Date.now() - now < 500);
console.log(cpuUsage(startUsage));
// { user: 514883, system: 11226 }- Returns: {string}
The process.cwd() method returns the current working directory of the Node.js
process.
import { cwd } from 'process';
console.log(`Current directory: ${cwd()}`);const { cwd } = require('process');
console.log(`Current directory: ${cwd()}`);- {number}
The port used by the Node.js debugger when enabled.
import process from 'process';
process.debugPort = 5858;const process = require('process');
process.debugPort = 5858;If the Node.js process is spawned with an IPC channel (see the Child Process
and Cluster documentation), the process.disconnect() method will close the
IPC channel to the parent process, allowing the child process to exit gracefully
once there are no other connections keeping it alive.
The effect of calling process.disconnect() is the same as calling
ChildProcess.disconnect() from the parent process.
If the Node.js process was not spawned with an IPC channel,
process.disconnect() will be undefined.
module{Object}filename{string}flags{os.constants.dlopen} Default:os.constants.dlopen.RTLD_LAZY
The process.dlopen() method allows dynamically loading shared objects. It is
primarily used by require() to load C++ Addons, and should not be used
directly, except in special cases. In other words, require() should be
preferred over process.dlopen() unless there are specific reasons such as
custom dlopen flags or loading from ES modules.
The flags argument is an integer that allows to specify dlopen
behavior. See the os.constants.dlopen documentation for details.
An important requirement when calling process.dlopen() is that the module
instance must be passed. Functions exported by the C++ Addon are then
accessible via module.exports.
The example below shows how to load a C++ Addon, named local.node,
that exports a foo function. All the symbols are loaded before
the call returns, by passing the RTLD_NOW constant. In this example
the constant is assumed to be available.
import { dlopen } from 'process';
import { constants } from 'os';
import { fileURLToPath } from 'url';
const module = { exports: {} };
dlopen(module, fileURLToPath(new URL('local.node', import.meta.url)),
constants.dlopen.RTLD_NOW);
module.exports.foo();const { dlopen } = require('process');
const { constants } = require('os');
const { join } = require('path');
const module = { exports: {} };
dlopen(module, join(__dirname, 'local.node'), constants.dlopen.RTLD_NOW);
module.exports.foo();warning{string|Error} The warning to emit.options{Object}type{string} Whenwarningis aString,typeis the name to use for the type of warning being emitted. Default:'Warning'.code{string} A unique identifier for the warning instance being emitted.ctor{Function} Whenwarningis aString,ctoris an optional function used to limit the generated stack trace. Default:process.emitWarning.detail{string} Additional text to include with the error.
The process.emitWarning() method can be used to emit custom or application
specific process warnings. These can be listened for by adding a handler to the
'warning' event.
import { emitWarning } from 'process';
// Emit a warning with a code and additional detail.
emitWarning('Something happened!', {
code: 'MY_WARNING',
detail: 'This is some additional information'
});
// Emits:
// (node:56338) [MY_WARNING] Warning: Something happened!
// This is some additional informationconst { emitWarning } = require('process');
// Emit a warning with a code and additional detail.
emitWarning('Something happened!', {
code: 'MY_WARNING',
detail: 'This is some additional information'
});
// Emits:
// (node:56338) [MY_WARNING] Warning: Something happened!
// This is some additional informationIn this example, an Error object is generated internally by
process.emitWarning() and passed through to the
'warning' handler.
import process from 'process';
process.on('warning', (warning) => {
console.warn(warning.name); // 'Warning'
console.warn(warning.message); // 'Something happened!'
console.warn(warning.code); // 'MY_WARNING'
console.warn(warning.stack); // Stack trace
console.warn(warning.detail); // 'This is some additional information'
});const process = require('process');
process.on('warning', (warning) => {
console.warn(warning.name); // 'Warning'
console.warn(warning.message); // 'Something happened!'
console.warn(warning.code); // 'MY_WARNING'
console.warn(warning.stack); // Stack trace
console.warn(warning.detail); // 'This is some additional information'
});If warning is passed as an Error object, the options argument is ignored.
warning{string|Error} The warning to emit.type{string} Whenwarningis aString,typeis the name to use for the type of warning being emitted. Default:'Warning'.code{string} A unique identifier for the warning instance being emitted.ctor{Function} Whenwarningis aString,ctoris an optional function used to limit the generated stack trace. Default:process.emitWarning.
The process.emitWarning() method can be used to emit custom or application
specific process warnings. These can be listened for by adding a handler to the
'warning' event.
import { emitWarning } from 'process';
// Emit a warning using a string.
emitWarning('Something happened!');
// Emits: (node: 56338) Warning: Something happened!const { emitWarning } = require('process');
// Emit a warning using a string.
emitWarning('Something happened!');
// Emits: (node: 56338) Warning: Something happened!import { emitWarning } from 'process';
// Emit a warning using a string and a type.
emitWarning('Something Happened!', 'CustomWarning');
// Emits: (node:56338) CustomWarning: Something Happened!const { emitWarning } = require('process');
// Emit a warning using a string and a type.
emitWarning('Something Happened!', 'CustomWarning');
// Emits: (node:56338) CustomWarning: Something Happened!import { emitWarning } from 'process';
emitWarning('Something happened!', 'CustomWarning', 'WARN001');
// Emits: (node:56338) [WARN001] CustomWarning: Something happened!const { emitWarning } = require('process');
process.emitWarning('Something happened!', 'CustomWarning', 'WARN001');
// Emits: (node:56338) [WARN001] CustomWarning: Something happened!In each of the previous examples, an Error object is generated internally by
process.emitWarning() and passed through to the 'warning'
handler.
import process from 'process';
process.on('warning', (warning) => {
console.warn(warning.name);
console.warn(warning.message);
console.warn(warning.code);
console.warn(warning.stack);
});const process = require('process');
process.on('warning', (warning) => {
console.warn(warning.name);
console.warn(warning.message);
console.warn(warning.code);
console.warn(warning.stack);
});If warning is passed as an Error object, it will be passed through to the
'warning' event handler unmodified (and the optional type,
code and ctor arguments will be ignored):
import { emitWarning } from 'process';
// Emit a warning using an Error object.
const myWarning = new Error('Something happened!');
// Use the Error name property to specify the type name
myWarning.name = 'CustomWarning';
myWarning.code = 'WARN001';
emitWarning(myWarning);
// Emits: (node:56338) [WARN001] CustomWarning: Something happened!const { emitWarning } = require('process');
// Emit a warning using an Error object.
const myWarning = new Error('Something happened!');
// Use the Error name property to specify the type name
myWarning.name = 'CustomWarning';
myWarning.code = 'WARN001';
emitWarning(myWarning);
// Emits: (node:56338) [WARN001] CustomWarning: Something happened!A TypeError is thrown if warning is anything other than a string or Error
object.
While process warnings use Error objects, the process warning
mechanism is not a replacement for normal error handling mechanisms.
The following additional handling is implemented if the warning type is
'DeprecationWarning':
- If the
--throw-deprecationcommand-line flag is used, the deprecation warning is thrown as an exception rather than being emitted as an event. - If the
--no-deprecationcommand-line flag is used, the deprecation warning is suppressed. - If the
--trace-deprecationcommand-line flag is used, the deprecation warning is printed tostderralong with the full stack trace.
As a best practice, warnings should be emitted only once per process. To do
so, it is recommended to place the emitWarning() behind a simple boolean
flag as illustrated in the example below:
import { emitWarning } from 'process';
function emitMyWarning() {
if (!emitMyWarning.warned) {
emitMyWarning.warned = true;
emitWarning('Only warn once!');
}
}
emitMyWarning();
// Emits: (node: 56339) Warning: Only warn once!
emitMyWarning();
// Emits nothingconst { emitWarning } = require('process');
function emitMyWarning() {
if (!emitMyWarning.warned) {
emitMyWarning.warned = true;
emitWarning('Only warn once!');
}
}
emitMyWarning();
// Emits: (node: 56339) Warning: Only warn once!
emitMyWarning();
// Emits nothing- {Object}
The process.env property returns an object containing the user environment.
See environ(7).
An example of this object looks like:
{
TERM: 'xterm-256color',
SHELL: '/usr/local/bin/bash',
USER: 'maciej',
PATH: '~/.bin/:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin',
PWD: '/Users/maciej',
EDITOR: 'vim',
SHLVL: '1',
HOME: '/Users/maciej',
LOGNAME: 'maciej',
_: '/usr/local/bin/node'
}It is possible to modify this object, but such modifications will not be
reflected outside the Node.js process, or (unless explicitly requested)
to other Worker threads.
In other words, the following example would not work:
$ node -e 'process.env.foo = "bar"' && echo $fooWhile the following will:
import { env } from 'process';
env.foo = 'bar';
console.log(env.foo);const { env } = require('process');
env.foo = 'bar';
console.log(env.foo);Assigning a property on process.env will implicitly convert the value
to a string. This behavior is deprecated. Future versions of Node.js may
throw an error when the value is not a string, number, or boolean.
import { env } from 'process';
env.test = null;
console.log(env.test);
// => 'null'
env.test = undefined;
console.log(env.test);
// => 'undefined'const { env } = require('process');
env.test = null;
console.log(env.test);
// => 'null'
env.test = undefined;
console.log(env.test);
// => 'undefined'Use delete to delete a property from process.env.
import { env } from 'process';
env.TEST = 1;
delete env.TEST;
console.log(env.TEST);
// => undefinedconst { env } = require('process');
env.TEST = 1;
delete env.TEST;
console.log(env.TEST);
// => undefinedOn Windows operating systems, environment variables are case-insensitive.
import { env } from 'process';
env.TEST = 1;
console.log(env.test);
// => 1const { env } = require('process');
env.TEST = 1;
console.log(env.test);
// => 1Unless explicitly specified when creating a Worker instance,
each Worker thread has its own copy of process.env, based on its
parent thread’s process.env, or whatever was specified as the env option
to the Worker constructor. Changes to process.env will not be visible
across Worker threads, and only the main thread can make changes that
are visible to the operating system or to native add-ons.
- {string[]}
The process.execArgv property returns the set of Node.js-specific command-line
options passed when the Node.js process was launched. These options do not
appear in the array returned by the process.argv property, and do not
include the Node.js executable, the name of the script, or any options following
the script name. These options are useful in order to spawn child processes with
the same execution environment as the parent.
$ node --harmony script.js --versionResults in process.execArgv:
['--harmony']And process.argv:
['/usr/local/bin/node', 'script.js', '--version']Refer to Worker constructor for the detailed behavior of worker
threads with this property.
- {string}
The process.execPath property returns the absolute pathname of the executable
that started the Node.js process. Symbolic links, if any, are resolved.
'/usr/local/bin/node'code{integer} The exit code. Default:0.
The process.exit() method instructs Node.js to terminate the process
synchronously with an exit status of code. If code is omitted, exit uses
either the 'success' code 0 or the value of process.exitCode if it has been
set. Node.js will not terminate until all the 'exit' event listeners are
called.
To exit with a 'failure' code:
import { exit } from 'process';
exit(1);const { exit } = require('process');
exit(1);The shell that executed Node.js should see the exit code as 1.
Calling process.exit() will force the process to exit as quickly as possible
even if there are still asynchronous operations pending that have not yet
completed fully, including I/O operations to process.stdout and
process.stderr.
In most situations, it is not actually necessary to call process.exit()
explicitly. The Node.js process will exit on its own if there is no additional
work pending in the event loop. The process.exitCode property can be set to
tell the process which exit code to use when the process exits gracefully.
For instance, the following example illustrates a misuse of the
process.exit() method that could lead to data printed to stdout being
truncated and lost:
import { exit } from 'process';
// This is an example of what *not* to do:
if (someConditionNotMet()) {
printUsageToStdout();
exit(1);
}const { exit } = require('process');
// This is an example of what *not* to do:
if (someConditionNotMet()) {
printUsageToStdout();
exit(1);
}The reason this is problematic is because writes to process.stdout in Node.js
are sometimes asynchronous and may occur over multiple ticks of the Node.js
event loop. Calling process.exit(), however, forces the process to exit
before those additional writes to stdout can be performed.
Rather than calling process.exit() directly, the code should set the
process.exitCode and allow the process to exit naturally by avoiding
scheduling any additional work for the event loop:
import process from 'process';
// How to properly set the exit code while letting
// the process exit gracefully.
if (someConditionNotMet()) {
printUsageToStdout();
process.exitCode = 1;
}const process = require('process');
// How to properly set the exit code while letting
// the process exit gracefully.
if (someConditionNotMet()) {
printUsageToStdout();
process.exitCode = 1;
}If it is necessary to terminate the Node.js process due to an error condition,
throwing an uncaught error and allowing the process to terminate accordingly
is safer than calling process.exit().
In Worker threads, this function stops the current thread rather
than the current process.
- {integer}
A number which will be the process exit code, when the process either
exits gracefully, or is exited via process.exit() without specifying
a code.
Specifying a code to process.exit(code) will override any
previous setting of process.exitCode.
Stability: 1 - Experimental
- Returns: {string[]}
The process.getActiveResourcesInfo() method returns an array of strings
containing the types of the active resources that are currently keeping the
event loop alive.
import { getActiveResourcesInfo } from 'process';
import { setTimeout } from 'timers';
console.log('Before:', getActiveResourcesInfo());
setTimeout(() => {}, 1000);
console.log('After:', getActiveResourcesInfo());
// Prints:
// Before: [ 'CloseReq', 'TTYWrap', 'TTYWrap', 'TTYWrap' ]
// After: [ 'CloseReq', 'TTYWrap', 'TTYWrap', 'TTYWrap', 'Timeout' ]const { getActiveResourcesInfo } = require('process');
const { setTimeout } = require('timers');
console.log('Before:', getActiveResourcesInfo());
setTimeout(() => {}, 1000);
console.log('After:', getActiveResourcesInfo());
// Prints:
// Before: [ 'TTYWrap', 'TTYWrap', 'TTYWrap' ]
// After: [ 'TTYWrap', 'TTYWrap', 'TTYWrap', 'Timeout' ]The process.getegid() method returns the numerical effective group identity
of the Node.js process. (See getegid(2).)
import process from 'process';
if (process.getegid) {
console.log(`Current gid: ${process.getegid()}`);
}const process = require('process');
if (process.getegid) {
console.log(`Current gid: ${process.getegid()}`);
}This function is only available on POSIX platforms (i.e. not Windows or Android).
- Returns: {Object}
The process.geteuid() method returns the numerical effective user identity of
the process. (See geteuid(2).)
import process from 'process';
if (process.geteuid) {
console.log(`Current uid: ${process.geteuid()}`);
}const process = require('process');
if (process.geteuid) {
console.log(`Current uid: ${process.geteuid()}`);
}This function is only available on POSIX platforms (i.e. not Windows or Android).
- Returns: {Object}
The process.getgid() method returns the numerical group identity of the
process. (See getgid(2).)
import process from 'process';
if (process.getgid) {
console.log(`Current gid: ${process.getgid()}`);
}const process = require('process');
if (process.getgid) {
console.log(`Current gid: ${process.getgid()}`);
}This function is only available on POSIX platforms (i.e. not Windows or Android).
- Returns: {integer[]}
The process.getgroups() method returns an array with the supplementary group
IDs. POSIX leaves it unspecified if the effective group ID is included but
Node.js ensures it always is.
import process from 'process';
if (process.getgroups) {
console.log(process.getgroups()); // [ 16, 21, 297 ]
}const process = require('process');
if (process.getgroups) {
console.log(process.getgroups()); // [ 16, 21, 297 ]
}This function is only available on POSIX platforms (i.e. not Windows or Android).
- Returns: {integer}
The process.getuid() method returns the numeric user identity of the process.
(See getuid(2).)
import process from 'process';
if (process.getuid) {
console.log(`Current uid: ${process.getuid()}`);
}const process = require('process');
if (process.getuid) {
console.log(`Current uid: ${process.getuid()}`);
}This function is only available on POSIX platforms (i.e. not Windows or Android).
- Returns: {boolean}
Indicates whether a callback has been set using
process.setUncaughtExceptionCaptureCallback().
Stability: 3 - Legacy. Use
process.hrtime.bigint()instead.
time{integer[]} The result of a previous call toprocess.hrtime()- Returns: {integer[]}
This is the legacy version of process.hrtime.bigint()
before bigint was introduced in JavaScript.
The process.hrtime() method returns the current high-resolution real time
in a [seconds, nanoseconds] tuple Array, where nanoseconds is the
remaining part of the real time that can't be represented in second precision.
time is an optional parameter that must be the result of a previous
process.hrtime() call to diff with the current time. If the parameter
passed in is not a tuple Array, a TypeError will be thrown. Passing in a
user-defined array instead of the result of a previous call to
process.hrtime() will lead to undefined behavior.
These times are relative to an arbitrary time in the past, and not related to the time of day and therefore not subject to clock drift. The primary use is for measuring performance between intervals:
import { hrtime } from 'process';
const NS_PER_SEC = 1e9;
const time = hrtime();
// [ 1800216, 25 ]
setTimeout(() => {
const diff = hrtime(time);
// [ 1, 552 ]
console.log(`Benchmark took ${diff[0] * NS_PER_SEC + diff[1]} nanoseconds`);
// Benchmark took 1000000552 nanoseconds
}, 1000);const { hrtime } = require('process');
const NS_PER_SEC = 1e9;
const time = hrtime();
// [ 1800216, 25 ]
setTimeout(() => {
const diff = hrtime(time);
// [ 1, 552 ]
console.log(`Benchmark took ${diff[0] * NS_PER_SEC + diff[1]} nanoseconds`);
// Benchmark took 1000000552 nanoseconds
}, 1000);- Returns: {bigint}
The bigint version of the process.hrtime() method returning the
current high-resolution real time in nanoseconds as a bigint.
Unlike process.hrtime(), it does not support an additional time
argument since the difference can just be computed directly
by subtraction of the two bigints.
import { hrtime } from 'process';
const start = hrtime.bigint();
// 191051479007711n
setTimeout(() => {
const end = hrtime.bigint();
// 191052633396993n
console.log(`Benchmark took ${end - start} nanoseconds`);
// Benchmark took 1154389282 nanoseconds
}, 1000);const { hrtime } = require('process');
const start = hrtime.bigint();
// 191051479007711n
setTimeout(() => {
const end = hrtime.bigint();
// 191052633396993n
console.log(`Benchmark took ${end - start} nanoseconds`);
// Benchmark took 1154389282 nanoseconds
}, 1000);user{string|number} The user name or numeric identifier.extraGroup{string|number} A group name or numeric identifier.
The process.initgroups() method reads the /etc/group file and initializes
the group access list, using all groups of which the user is a member. This is
a privileged operation that requires that the Node.js process either have root
access or the CAP_SETGID capability.
Use care when dropping privileges:
import { getgroups, initgroups, setgid } from 'process';
console.log(getgroups()); // [ 0 ]
initgroups('nodeuser', 1000); // switch user
console.log(getgroups()); // [ 27, 30, 46, 1000, 0 ]
setgid(1000); // drop root gid
console.log(getgroups()); // [ 27, 30, 46, 1000 ]const { getgroups, initgroups, setgid } = require('process');
console.log(getgroups()); // [ 0 ]
initgroups('nodeuser', 1000); // switch user
console.log(getgroups()); // [ 27, 30, 46, 1000, 0 ]
setgid(1000); // drop root gid
console.log(getgroups()); // [ 27, 30, 46, 1000 ]This function is only available on POSIX platforms (i.e. not Windows or
Android).
This feature is not available in Worker threads.
pid{number} A process IDsignal{string|number} The signal to send, either as a string or number. Default:'SIGTERM'.
The process.kill() method sends the signal to the process identified by
pid.
Signal names are strings such as 'SIGINT' or 'SIGHUP'. See Signal Events
and kill(2) for more information.
This method will throw an error if the target pid does not exist. As a special
case, a signal of 0 can be used to test for the existence of a process.
Windows platforms will throw an error if the pid is used to kill a process
group.
Even though the name of this function is process.kill(), it is really just a
signal sender, like the kill system call. The signal sent may do something
other than kill the target process.
import process, { kill } from 'process';
process.on('SIGHUP', () => {
console.log('Got SIGHUP signal.');
});
setTimeout(() => {
console.log('Exiting.');
process.exit(0);
}, 100);
kill(process.pid, 'SIGHUP');const process = require('process');
process.on('SIGHUP', () => {
console.log('Got SIGHUP signal.');
});
setTimeout(() => {
console.log('Exiting.');
process.exit(0);
}, 100);
process.kill(process.pid, 'SIGHUP');When SIGUSR1 is received by a Node.js process, Node.js will start the
debugger. See Signal Events.
Stability: 0 - Deprecated: Use
require.maininstead.
- {Object}
The process.mainModule property provides an alternative way of retrieving
require.main. The difference is that if the main module changes at
runtime, require.main may still refer to the original main module in
modules that were required before the change occurred. Generally, it's
safe to assume that the two refer to the same module.
As with require.main, process.mainModule will be undefined if there
is no entry script.
- Returns: {Object}
rss{integer}heapTotal{integer}heapUsed{integer}external{integer}arrayBuffers{integer}
Returns an object describing the memory usage of the Node.js process measured in bytes.
import { memoryUsage } from 'process';
console.log(memoryUsage());
// Prints:
// {
// rss: 4935680,
// heapTotal: 1826816,
// heapUsed: 650472,
// external: 49879,
// arrayBuffers: 9386
// }const { memoryUsage } = require('process');
console.log(memoryUsage());
// Prints:
// {
// rss: 4935680,
// heapTotal: 1826816,
// heapUsed: 650472,
// external: 49879,
// arrayBuffers: 9386
// }heapTotalandheapUsedrefer to V8's memory usage.externalrefers to the memory usage of C++ objects bound to JavaScript objects managed by V8.rss, Resident Set Size, is the amount of space occupied in the main memory device (that is a subset of the total allocated memory) for the process, including all C++ and JavaScript objects and code.arrayBuffersrefers to memory allocated forArrayBuffers andSharedArrayBuffers, including all Node.jsBuffers. This is also included in theexternalvalue. When Node.js is used as an embedded library, this value may be0because allocations forArrayBuffers may not be tracked in that case.
When using Worker threads, rss will be a value that is valid for the
entire process, while the other fields will only refer to the current thread.
The process.memoryUsage() method iterates over each page to gather
information about memory usage which might be slow depending on the
program memory allocations.
- Returns: {integer}
The process.memoryUsage.rss() method returns an integer representing the
Resident Set Size (RSS) in bytes.
The Resident Set Size, is the amount of space occupied in the main memory device (that is a subset of the total allocated memory) for the process, including all C++ and JavaScript objects and code.
This is the same value as the rss property provided by process.memoryUsage()
but process.memoryUsage.rss() is faster.
import { memoryUsage } from 'process';
console.log(memoryUsage.rss());
// 35655680const { rss } = require('process');
console.log(memoryUsage.rss());
// 35655680callback{Function}...args{any} Additional arguments to pass when invoking thecallback
process.nextTick() adds callback to the "next tick queue". This queue is
fully drained after the current operation on the JavaScript stack runs to
completion and before the event loop is allowed to continue. It's possible to
create an infinite loop if one were to recursively call process.nextTick().
See the Event Loop guide for more background.
import { nextTick } from 'process';
console.log('start');
nextTick(() => {
console.log('nextTick callback');
});
console.log('scheduled');
// Output:
// start
// scheduled
// nextTick callbackconst { nextTick } = require('process');
console.log('start');
nextTick(() => {
console.log('nextTick callback');
});
console.log('scheduled');
// Output:
// start
// scheduled
// nextTick callbackThis is important when developing APIs in order to give users the opportunity to assign event handlers after an object has been constructed but before any I/O has occurred:
import { nextTick } from 'process';
function MyThing(options) {
this.setupOptions(options);
nextTick(() => {
this.startDoingStuff();
});
}
const thing = new MyThing();
thing.getReadyForStuff();
// thing.startDoingStuff() gets called now, not before.const { nextTick } = require('process');
function MyThing(options) {
this.setupOptions(options);
nextTick(() => {
this.startDoingStuff();
});
}
const thing = new MyThing();
thing.getReadyForStuff();
// thing.startDoingStuff() gets called now, not before.It is very important for APIs to be either 100% synchronous or 100% asynchronous. Consider this example:
// WARNING! DO NOT USE! BAD UNSAFE HAZARD!
function maybeSync(arg, cb) {
if (arg) {
cb();
return;
}
fs.stat('file', cb);
}This API is hazardous because in the following case:
const maybeTrue = Math.random() > 0.5;
maybeSync(maybeTrue, () => {
foo();
});
bar();It is not clear whether foo() or bar() will be called first.
The following approach is much better:
import { nextTick } from 'process';
function definitelyAsync(arg, cb) {
if (arg) {
nextTick(cb);
return;
}
fs.stat('file', cb);
}const { nextTick } = require('process');
function definitelyAsync(arg, cb) {
if (arg) {
nextTick(cb);
return;
}
fs.stat('file', cb);
}The queueMicrotask() API is an alternative to process.nextTick() that
also defers execution of a function using the same microtask queue used to
execute the then, catch, and finally handlers of resolved promises. Within
Node.js, every time the "next tick queue" is drained, the microtask queue
is drained immediately after.
import { nextTick } from 'process';
Promise.resolve().then(() => console.log(2));
queueMicrotask(() => console.log(3));
nextTick(() => console.log(1));
// Output:
// 1
// 2
// 3const { nextTick } = require('process');
Promise.resolve().then(() => console.log(2));
queueMicrotask(() => console.log(3));
nextTick(() => console.log(1));
// Output:
// 1
// 2
// 3For most userland use cases, the queueMicrotask() API provides a portable
and reliable mechanism for deferring execution that works across multiple
JavaScript platform environments and should be favored over process.nextTick().
In simple scenarios, queueMicrotask() can be a drop-in replacement for
process.nextTick().
console.log('start');
queueMicrotask(() => {
console.log('microtask callback');
});
console.log('scheduled');
// Output:
// start
// scheduled
// microtask callbackOne note-worthy difference between the two APIs is that process.nextTick()
allows specifying additional values that will be passed as arguments to the
deferred function when it is called. Achieving the same result with
queueMicrotask() requires using either a closure or a bound function:
function deferred(a, b) {
console.log('microtask', a + b);
}
console.log('start');
queueMicrotask(deferred.bind(undefined, 1, 2));
console.log('scheduled');
// Output:
// start
// scheduled
// microtask 3There are minor differences in the way errors raised from within the next tick
queue and microtask queue are handled. Errors thrown within a queued microtask
callback should be handled within the queued callback when possible. If they are
not, the process.on('uncaughtException') event handler can be used to capture
and handle the errors.
When in doubt, unless the specific capabilities of process.nextTick() are
needed, use queueMicrotask().
- {boolean}
The process.noDeprecation property indicates whether the --no-deprecation
flag is set on the current Node.js process. See the documentation for
the 'warning' event and the
emitWarning() method for more information about this
flag's behavior.
- {integer}
The process.pid property returns the PID of the process.
import { pid } from 'process';
console.log(`This process is pid ${pid}`);const { pid } = require('process');
console.log(`This process is pid ${pid}`);- {string}
The process.platform property returns a string identifying the operating
system platform for which the Node.js binary was compiled.
Currently possible values are:
'aix''darwin''freebsd''linux''openbsd''sunos''win32'
import { platform } from 'process';
console.log(`This platform is ${platform}`);const { platform } = require('process');
console.log(`This platform is ${platform}`);The value 'android' may also be returned if the Node.js is built on the
Android operating system. However, Android support in Node.js
is experimental.
- {integer}
The process.ppid property returns the PID of the parent of the
current process.
import { ppid } from 'process';
console.log(`The parent process is pid ${ppid}`);const { ppid } = require('process');
console.log(`The parent process is pid ${ppid}`);- {Object}
The process.release property returns an Object containing metadata related
to the current release, including URLs for the source tarball and headers-only
tarball.
process.release contains the following properties:
name{string} A value that will always be'node'.sourceUrl{string} an absolute URL pointing to a.tar.gzfile containing the source code of the current release.headersUrl{string} an absolute URL pointing to a.tar.gzfile containing only the source header files for the current release. This file is significantly smaller than the full source file and can be used for compiling Node.js native add-ons.libUrl{string} an absolute URL pointing to anode.libfile matching the architecture and version of the current release. This file is used for compiling Node.js native add-ons. This property is only present on Windows builds of Node.js and will be missing on all other platforms.lts{string} a string label identifying the LTS label for this release. This property only exists for LTS releases and isundefinedfor all other release types, including Current releases. Valid values include the LTS Release code names (including those that are no longer supported).'Dubnium'for the 10.x LTS line beginning with 10.13.0.'Erbium'for the 12.x LTS line beginning with 12.13.0. For other LTS Release code names, see Node.js Changelog Archive
{
name: 'node',
lts: 'Erbium',
sourceUrl: 'https://nodejs.org/download/release/v12.18.1/node-v12.18.1.tar.gz',
headersUrl: 'https://nodejs.org/download/release/v12.18.1/node-v12.18.1-headers.tar.gz',
libUrl: 'https://nodejs.org/download/release/v12.18.1/win-x64/node.lib'
}In custom builds from non-release versions of the source tree, only the
name property may be present. The additional properties should not be
relied upon to exist.
- {Object}
process.report is an object whose methods are used to generate diagnostic
reports for the current process. Additional documentation is available in the
report documentation.
- {boolean}
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.
import { report } from 'process';
console.log(`Reports are compact? ${report.compact}`);const { report } = require('process');
console.log(`Reports are compact? ${report.compact}`);- {string}
Directory where the report is written. The default value is the empty string, indicating that reports are written to the current working directory of the Node.js process.
import { report } from 'process';
console.log(`Report directory is ${report.directory}`);const { report } = require('process');
console.log(`Report directory is ${report.directory}`);- {string}
Filename where the report is written. If set to the empty string, the output filename will be comprised of a timestamp, PID, and sequence number. The default value is the empty string.
import { report } from 'process';
console.log(`Report filename is ${report.filename}`);const { report } = require('process');
console.log(`Report filename is ${report.filename}`);err{Error} A custom error used for reporting the JavaScript stack.- Returns: {Object}
Returns a JavaScript Object representation of a diagnostic report for the
running process. The report's JavaScript stack trace is taken from err, if
present.
import { report } from 'process';
const data = report.getReport();
console.log(data.header.nodejsVersion);
// Similar to process.report.writeReport()
import fs from 'fs';
fs.writeFileSync('my-report.log', util.inspect(data), 'utf8');const { report } = require('process');
const data = report.getReport();
console.log(data.header.nodejsVersion);
// Similar to process.report.writeReport()
const fs = require('fs');
fs.writeFileSync('my-report.log', util.inspect(data), 'utf8');Additional documentation is available in the report documentation.
- {boolean}
If true, a diagnostic report is generated on fatal errors, such as out of
memory errors or failed C++ assertions.
import { report } from 'process';
console.log(`Report on fatal error: ${report.reportOnFatalError}`);const { report } = require('process');
console.log(`Report on fatal error: ${report.reportOnFatalError}`);- {boolean}
If true, a diagnostic report is generated when the process receives the
signal specified by process.report.signal.
import { report } from 'process';
console.log(`Report on signal: ${report.reportOnSignal}`);const { report } = require('process');
console.log(`Report on signal: ${report.reportOnSignal}`);- {boolean}
If true, a diagnostic report is generated on uncaught exception.
import { report } from 'process';
console.log(`Report on exception: ${report.reportOnUncaughtException}`);const { report } = require('process');
console.log(`Report on exception: ${report.reportOnUncaughtException}`);- {string}
The signal used to trigger the creation of a diagnostic report. Defaults to
'SIGUSR2'.
import { report } from 'process';
console.log(`Report signal: ${report.signal}`);const { report } = require('process');
console.log(`Report signal: ${report.signal}`);-
filename{string} Name of the file where the report is written. This should be a relative path, that will be appended to the directory specified inprocess.report.directory, or the current working directory of the Node.js process, if unspecified. -
err{Error} A custom error used for reporting the JavaScript stack. -
Returns: {string} Returns the filename of the generated report.
Writes a diagnostic report to a file. If filename is not provided, the default
filename includes the date, time, PID, and a sequence number. The report's
JavaScript stack trace is taken from err, if present.
import { report } from 'process';
report.writeReport();const { report } = require('process');
report.writeReport();Additional documentation is available in the report documentation.
- Returns: {Object} the resource usage for the current process. All of these
values come from the
uv_getrusagecall which returns auv_rusage_tstruct.userCPUTime{integer} maps toru_utimecomputed in microseconds. It is the same value asprocess.cpuUsage().user.systemCPUTime{integer} maps toru_stimecomputed in microseconds. It is the same value asprocess.cpuUsage().system.maxRSS{integer} maps toru_maxrsswhich is the maximum resident set size used in kilobytes.sharedMemorySize{integer} maps toru_ixrssbut is not supported by any platform.unsharedDataSize{integer} maps toru_idrssbut is not supported by any platform.unsharedStackSize{integer} maps toru_isrssbut is not supported by any platform.minorPageFault{integer} maps toru_minfltwhich is the number of minor page faults for the process, see this article for more details.majorPageFault{integer} maps toru_majfltwhich is the number of major page faults for the process, see this article for more details. This field is not supported on Windows.swappedOut{integer} maps toru_nswapbut is not supported by any platform.fsRead{integer} maps toru_inblockwhich is the number of times the file system had to perform input.fsWrite{integer} maps toru_oublockwhich is the number of times the file system had to perform output.ipcSent{integer} maps toru_msgsndbut is not supported by any platform.ipcReceived{integer} maps toru_msgrcvbut is not supported by any platform.signalsCount{integer} maps toru_nsignalsbut is not supported by any platform.voluntaryContextSwitches{integer} maps toru_nvcswwhich is the number of times a CPU context switch resulted due to a process voluntarily giving up the processor before its time slice was completed (usually to await availability of a resource). This field is not supported on Windows.involuntaryContextSwitches{integer} maps toru_nivcswwhich is the number of times a CPU context switch resulted due to a higher priority process becoming runnable or because the current process exceeded its time slice. This field is not supported on Windows.
import { resourceUsage } from 'process';
console.log(resourceUsage());
/*
Will output:
{
userCPUTime: 82872,
systemCPUTime: 4143,
maxRSS: 33164,
sharedMemorySize: 0,
unsharedDataSize: 0,
unsharedStackSize: 0,
minorPageFault: 2469,
majorPageFault: 0,
swappedOut: 0,
fsRead: 0,
fsWrite: 8,
ipcSent: 0,
ipcReceived: 0,
signalsCount: 0,
voluntaryContextSwitches: 79,
involuntaryContextSwitches: 1
}
*/const { resourceUsage } = require('process');
console.log(resourceUsage());
/*
Will output:
{
userCPUTime: 82872,
systemCPUTime: 4143,
maxRSS: 33164,
sharedMemorySize: 0,
unsharedDataSize: 0,
unsharedStackSize: 0,
minorPageFault: 2469,
majorPageFault: 0,
swappedOut: 0,
fsRead: 0,
fsWrite: 8,
ipcSent: 0,
ipcReceived: 0,
signalsCount: 0,
voluntaryContextSwitches: 79,
involuntaryContextSwitches: 1
}
*/message{Object}sendHandle{net.Server|net.Socket}options{Object} used to parameterize the sending of certain types of handles.optionssupports the following properties:keepOpen{boolean} A value that can be used when passing instances ofnet.Socket. Whentrue, the socket is kept open in the sending process. Default:false.
callback{Function}- Returns: {boolean}
If Node.js is spawned with an IPC channel, the process.send() method can be
used to send messages to the parent process. Messages will be received as a
'message' event on the parent's ChildProcess object.
If Node.js was not spawned with an IPC channel, process.send will be
undefined.
The message goes through serialization and parsing. The resulting message might not be the same as what is originally sent.
id{string|number} A group name or ID
The process.setegid() method sets the effective group identity of the process.
(See setegid(2).) The id can be passed as either a numeric ID or a group
name string. If a group name is specified, this method blocks while resolving
the associated a numeric ID.
import process from 'process';
if (process.getegid && process.setegid) {
console.log(`Current gid: ${process.getegid()}`);
try {
process.setegid(501);
console.log(`New gid: ${process.getegid()}`);
} catch (err) {
console.log(`Failed to set gid: ${err}`);
}
}const process = require('process');
if (process.getegid && process.setegid) {
console.log(`Current gid: ${process.getegid()}`);
try {
process.setegid(501);
console.log(`New gid: ${process.getegid()}`);
} catch (err) {
console.log(`Failed to set gid: ${err}`);
}
}This function is only available on POSIX platforms (i.e. not Windows or
Android).
This feature is not available in Worker threads.
id{string|number} A user name or ID
The process.seteuid() method sets the effective user identity of the process.
(See seteuid(2).) The id can be passed as either a numeric ID or a username
string. If a username is specified, the method blocks while resolving the
associated numeric ID.
import process from 'process';
if (process.geteuid && process.seteuid) {
console.log(`Current uid: ${process.geteuid()}`);
try {
process.seteuid(501);
console.log(`New uid: ${process.geteuid()}`);
} catch (err) {
console.log(`Failed to set uid: ${err}`);
}
}const process = require('process');
if (process.geteuid && process.seteuid) {
console.log(`Current uid: ${process.geteuid()}`);
try {
process.seteuid(501);
console.log(`New uid: ${process.geteuid()}`);
} catch (err) {
console.log(`Failed to set uid: ${err}`);
}
}This function is only available on POSIX platforms (i.e. not Windows or
Android).
This feature is not available in Worker threads.
id{string|number} The group name or ID
The process.setgid() method sets the group identity of the process. (See
setgid(2).) The id can be passed as either a numeric ID or a group name
string. If a group name is specified, this method blocks while resolving the
associated numeric ID.
import process from 'process';
if (process.getgid && process.setgid) {
console.log(`Current gid: ${process.getgid()}`);
try {
process.setgid(501);
console.log(`New gid: ${process.getgid()}`);
} catch (err) {
console.log(`Failed to set gid: ${err}`);
}
}const process = require('process');
if (process.getgid && process.setgid) {
console.log(`Current gid: ${process.getgid()}`);
try {
process.setgid(501);
console.log(`New gid: ${process.getgid()}`);
} catch (err) {
console.log(`Failed to set gid: ${err}`);
}
}This function is only available on POSIX platforms (i.e. not Windows or
Android).
This feature is not available in Worker threads.
groups{integer[]}
The process.setgroups() method sets the supplementary group IDs for the
Node.js process. This is a privileged operation that requires the Node.js
process to have root or the CAP_SETGID capability.
The groups array can contain numeric group IDs, group names, or both.
import process from 'process';
if (process.getgroups && process.setgroups) {
try {
process.setgroups([501]);
console.log(process.getgroups()); // new groups
} catch (err) {
console.log(`Failed to set groups: ${err}`);
}
}const process = require('process');
if (process.getgroups && process.setgroups) {
try {
process.setgroups([501]);
console.log(process.getgroups()); // new groups
} catch (err) {
console.log(`Failed to set groups: ${err}`);
}
}This function is only available on POSIX platforms (i.e. not Windows or
Android).
This feature is not available in Worker threads.
id{integer | string}
The process.setuid(id) method sets the user identity of the process. (See
setuid(2).) The id can be passed as either a numeric ID or a username string.
If a username is specified, the method blocks while resolving the associated
numeric ID.
import process from 'process';
if (process.getuid && process.setuid) {
console.log(`Current uid: ${process.getuid()}`);
try {
process.setuid(501);
console.log(`New uid: ${process.getuid()}`);
} catch (err) {
console.log(`Failed to set uid: ${err}`);
}
}const process = require('process');
if (process.getuid && process.setuid) {
console.log(`Current uid: ${process.getuid()}`);
try {
process.setuid(501);
console.log(`New uid: ${process.getuid()}`);
} catch (err) {
console.log(`Failed to set uid: ${err}`);
}
}This function is only available on POSIX platforms (i.e. not Windows or
Android).
This feature is not available in Worker threads.
Stability: 1 - Experimental
val{boolean}
This function enables or disables the Source Map v3 support for stack traces.
It provides same features as launching Node.js process with commandline options
--enable-source-maps.
Only source maps in JavaScript files that are loaded after source maps has been enabled will be parsed and loaded.
fn{Function|null}
The process.setUncaughtExceptionCaptureCallback() function sets a function
that will be invoked when an uncaught exception occurs, which will receive the
exception value itself as its first argument.
If such a function is set, the 'uncaughtException' event will
not be emitted. If --abort-on-uncaught-exception was passed from the
command line or set through v8.setFlagsFromString(), the process will
not abort. Actions configured to take place on exceptions such as report
generations will be affected too
To unset the capture function,
process.setUncaughtExceptionCaptureCallback(null) may be used. Calling this
method with a non-null argument while another capture function is set will
throw an error.
Using this function is mutually exclusive with using the deprecated
domain built-in module.
- {Stream}
The process.stderr property returns a stream connected to
stderr (fd 2). It is a net.Socket (which is a Duplex
stream) unless fd 2 refers to a file, in which case it is
a Writable stream.
process.stderr differs from other Node.js streams in important ways. See
note on process I/O for more information.
- {number}
This property refers to the value of underlying file descriptor of
process.stderr. The value is fixed at 2. In Worker threads,
this field does not exist.
- {Stream}
The process.stdin property returns a stream connected to
stdin (fd 0). It is a net.Socket (which is a Duplex
stream) unless fd 0 refers to a file, in which case it is
a Readable stream.
For details of how to read from stdin see readable.read().
As a Duplex stream, process.stdin can also be used in "old" mode that
is compatible with scripts written for Node.js prior to v0.10.
For more information see Stream compatibility.
In "old" streams mode the stdin stream is paused by default, so one
must call process.stdin.resume() to read from it. Note also that calling
process.stdin.resume() itself would switch stream to "old" mode.
- {number}
This property refers to the value of underlying file descriptor of
process.stdin. The value is fixed at 0. In Worker threads,
this field does not exist.
- {Stream}
The process.stdout property returns a stream connected to
stdout (fd 1). It is a net.Socket (which is a Duplex
stream) unless fd 1 refers to a file, in which case it is
a Writable stream.
For example, to copy process.stdin to process.stdout:
import { stdin, stdout } from 'process';
stdin.pipe(stdout);const { stdin, stdout } = require('process');
stdin.pipe(stdout);process.stdout differs from other Node.js streams in important ways. See
note on process I/O for more information.
- {number}
This property refers to the value of underlying file descriptor of
process.stdout. The value is fixed at 1. In Worker threads,
this field does not exist.
process.stdout and process.stderr differ from other Node.js streams in
important ways:
- They are used internally by
console.log()andconsole.error(), respectively. - Writes may be synchronous depending on what the stream is connected to
and whether the system is Windows or POSIX:
- Files: synchronous on Windows and POSIX
- TTYs (Terminals): asynchronous on Windows, synchronous on POSIX
- Pipes (and sockets): synchronous on Windows, asynchronous on POSIX
These behaviors are partly for historical reasons, as changing them would create backward incompatibility, but they are also expected by some users.
Synchronous writes avoid problems such as output written with console.log() or
console.error() being unexpectedly interleaved, or not written at all if
process.exit() is called before an asynchronous write completes. See
process.exit() for more information.
Warning: Synchronous writes block the event loop until the write has completed. This can be near instantaneous in the case of output to a file, but under high system load, pipes that are not being read at the receiving end, or with slow terminals or file systems, its possible for the event loop to be blocked often enough and long enough to have severe negative performance impacts. This may not be a problem when writing to an interactive terminal session, but consider this particularly careful when doing production logging to the process output streams.
To check if a stream is connected to a TTY context, check the isTTY
property.
For instance:
$ node -p "Boolean(process.stdin.isTTY)"
true
$ echo "foo" | node -p "Boolean(process.stdin.isTTY)"
false
$ node -p "Boolean(process.stdout.isTTY)"
true
$ node -p "Boolean(process.stdout.isTTY)" | cat
falseSee the TTY documentation for more information.
- {boolean}
The initial value of process.throwDeprecation indicates whether the
--throw-deprecation flag is set on the current Node.js process.
process.throwDeprecation is mutable, so whether or not deprecation
warnings result in errors may be altered at runtime. See the
documentation for the 'warning' event and the
emitWarning() method for more information.
$ node --throw-deprecation -p "process.throwDeprecation"
true
$ node -p "process.throwDeprecation"
undefined
$ node
> process.emitWarning('test', 'DeprecationWarning');
undefined
> (node:26598) DeprecationWarning: test
> process.throwDeprecation = true;
true
> process.emitWarning('test', 'DeprecationWarning');
Thrown:
[DeprecationWarning: test] { name: 'DeprecationWarning' }- {string}
The process.title property returns the current process title (i.e. returns
the current value of ps). Assigning a new value to process.title modifies
the current value of ps.
When a new value is assigned, different platforms will impose different maximum
length restrictions on the title. Usually such restrictions are quite limited.
For instance, on Linux and macOS, process.title is limited to the size of the
binary name plus the length of the command-line arguments because setting the
process.title overwrites the argv memory of the process. Node.js v0.8
allowed for longer process title strings by also overwriting the environ
memory but that was potentially insecure and confusing in some (rather obscure)
cases.
Assigning a value to process.title might not result in an accurate label
within process manager applications such as macOS Activity Monitor or Windows
Services Manager.
- {boolean}
The process.traceDeprecation property indicates whether the
--trace-deprecation flag is set on the current Node.js process. See the
documentation for the 'warning' event and the
emitWarning() method for more information about this
flag's behavior.
Stability: 0 - Deprecated. Calling
process.umask()with no argument causes the process-wide umask to be written twice. This introduces a race condition between threads, and is a potential security vulnerability. There is no safe, cross-platform alternative API.
process.umask() returns the Node.js process's file mode creation mask. Child
processes inherit the mask from the parent process.
mask{string|integer}
process.umask(mask) sets the Node.js process's file mode creation mask. Child
processes inherit the mask from the parent process. Returns the previous mask.
import { umask } from 'process';
const newmask = 0o022;
const oldmask = umask(newmask);
console.log(
`Changed umask from ${oldmask.toString(8)} to ${newmask.toString(8)}`
);const { umask } = require('process');
const newmask = 0o022;
const oldmask = umask(newmask);
console.log(
`Changed umask from ${oldmask.toString(8)} to ${newmask.toString(8)}`
);In Worker threads, process.umask(mask) will throw an exception.
- Returns: {number}
The process.uptime() method returns the number of seconds the current Node.js
process has been running.
The return value includes fractions of a second. Use Math.floor() to get whole
seconds.
- {string}
The process.version property contains the Node.js version string.
import { version } from 'process';
console.log(`Version: ${version}`);
// Version: v14.8.0const { version } = require('process');
console.log(`Version: ${version}`);
// Version: v14.8.0To get the version string without the prepended v, use
process.versions.node.
- {Object}
The process.versions property returns an object listing the version strings of
Node.js and its dependencies. process.versions.modules indicates the current
ABI version, which is increased whenever a C++ API changes. Node.js will refuse
to load modules that were compiled against a different module ABI version.
import { versions } from 'process';
console.log(versions);const { versions } = require('process');
console.log(versions);Will generate an object similar to:
{ node: '11.13.0',
v8: '7.0.276.38-node.18',
uv: '1.27.0',
zlib: '1.2.11',
brotli: '1.0.7',
ares: '1.15.0',
modules: '67',
nghttp2: '1.34.0',
napi: '4',
llhttp: '1.1.1',
openssl: '1.1.1b',
cldr: '34.0',
icu: '63.1',
tz: '2018e',
unicode: '11.0' }Node.js will normally exit with a 0 status code when no more async
operations are pending. The following status codes are used in other
cases:
1Uncaught Fatal Exception: There was an uncaught exception, and it was not handled by a domain or an'uncaughtException'event handler.2: Unused (reserved by Bash for builtin misuse)3Internal JavaScript Parse Error: The JavaScript source code internal in the Node.js bootstrapping process caused a parse error. This is extremely rare, and generally can only happen during development of Node.js itself.4Internal JavaScript Evaluation Failure: The JavaScript source code internal in the Node.js bootstrapping process failed to return a function value when evaluated. This is extremely rare, and generally can only happen during development of Node.js itself.5Fatal Error: There was a fatal unrecoverable error in V8. Typically a message will be printed to stderr with the prefixFATAL ERROR.6Non-function Internal Exception Handler: There was an uncaught exception, but the internal fatal exception handler function was somehow set to a non-function, and could not be called.7Internal Exception Handler Run-Time Failure: There was an uncaught exception, and the internal fatal exception handler function itself threw an error while attempting to handle it. This can happen, for example, if an'uncaughtException'ordomain.on('error')handler throws an error.8: Unused. In previous versions of Node.js, exit code 8 sometimes indicated an uncaught exception.9Invalid Argument: Either an unknown option was specified, or an option requiring a value was provided without a value.10Internal JavaScript Run-Time Failure: The JavaScript source code internal in the Node.js bootstrapping process threw an error when the bootstrapping function was called. This is extremely rare, and generally can only happen during development of Node.js itself.12Invalid Debug Argument: The--inspectand/or--inspect-brkoptions were set, but the port number chosen was invalid or unavailable.13Unfinished Top-Level Await:awaitwas used outside of a function in the top-level code, but the passedPromisenever resolved.>128Signal Exits: If Node.js receives a fatal signal such asSIGKILLorSIGHUP, then its exit code will be128plus the value of the signal code. This is a standard POSIX practice, since exit codes are defined to be 7-bit integers, and signal exits set the high-order bit, and then contain the value of the signal code. For example, signalSIGABRThas value6, so the expected exit code will be128+6, or134.