Timers#
Source Code: lib/timers.js
The timer module exposes a global API for scheduling functions to
be called at some future period of time. Because the timer functions are
globals, there is no need to call require('node:timers') to use the API.
The timer functions within Node.js implement a similar API as the timers API
provided by Web Browsers but use a different internal implementation that is
built around the Node.js Event Loop.
Class: Immediate#
This object is created internally and is returned from setImmediate(). It
can be passed to clearImmediate() in order to cancel the scheduled
actions.
By default, when an immediate is scheduled, the Node.js event loop will continue
running as long as the immediate is active. The Immediate object returned by
setImmediate() exports both immediate.ref() and immediate.unref()
functions that can be used to control this default behavior.
immediate.hasRef()#
Added in: v11.0.0
If true, the Immediate object will keep the Node.js event loop active.
immediate.ref()#
Added in: v9.7.0
When called, requests that the Node.js event loop not exit so long as the
Immediate is active. Calling immediate.ref() multiple times will have no
effect.
By default, all Immediate objects are "ref'ed", making it normally unnecessary
to call immediate.ref() unless immediate.unref() had been called previously.
immediate.unref()#
Added in: v9.7.0
When called, the active Immediate object will not require the Node.js event
loop to remain active. If there is no other activity keeping the event loop
running, the process may exit before the Immediate object's callback is
invoked. Calling immediate.unref() multiple times will have no effect.
immediate[Symbol.dispose]()#
Added in: v20.5.0, v18.18.0
Cancels the immediate. This is similar to calling clearImmediate().
Class: Timeout#
This object is created internally and is returned from setTimeout() and
setInterval(). It can be passed to either clearTimeout() or
clearInterval() in order to cancel the scheduled actions.
By default, when a timer is scheduled using either setTimeout() or
setInterval(), the Node.js event loop will continue running as long as the
timer is active. Each of the Timeout objects returned by these functions
export both timeout.ref() and timeout.unref() functions that can be used to
control this default behavior.
timeout.close()#
Added in: v0.9.1
Cancels the timeout.
timeout.hasRef()#
Added in: v11.0.0
If true, the Timeout object will keep the Node.js event loop active.
timeout.ref()#
Added in: v0.9.1
When called, requests that the Node.js event loop not exit so long as the
Timeout is active. Calling timeout.ref() multiple times will have no effect.
By default, all Timeout objects are "ref'ed", making it normally unnecessary
to call timeout.ref() unless timeout.unref() had been called previously.
timeout.refresh()#
Added in: v10.2.0
Sets the timer's start time to the current time, and reschedules the timer to
call its callback at the previously specified duration adjusted to the current
time. This is useful for refreshing a timer without allocating a new
JavaScript object.
Using this on a timer that has already called its callback will reactivate the
timer.
timeout.unref()#
Added in: v0.9.1
When called, the active Timeout object will not require the Node.js event loop
to remain active. If there is no other activity keeping the event loop running,
the process may exit before the Timeout object's callback is invoked. Calling
timeout.unref() multiple times will have no effect.
timeout[Symbol.toPrimitive]()#
Added in: v14.9.0, v12.19.0
- Returns: <integer> a number that can be used to reference this
timeout
Coerce a Timeout to a primitive. The primitive can be used to
clear the Timeout. The primitive can only be used in the
same thread where the timeout was created. Therefore, to use it
across worker_threads it must first be passed to the correct
thread. This allows enhanced compatibility with browser
setTimeout() and setInterval() implementations.
timeout[Symbol.dispose]()#
Added in: v20.5.0, v18.18.0
Cancels the timeout.
Scheduling timers#
A timer in Node.js is an internal construct that calls a given function after
a certain period of time. When a timer's function is called varies depending on
which method was used to create the timer and what other work the Node.js
event loop is doing.
setImmediate(callback[, ...args])#
Schedules the "immediate" execution of the callback after I/O events'
callbacks.
When multiple calls to setImmediate() are made, the callback functions are
queued for execution in the order in which they are created. The entire callback
queue is processed every event loop iteration. If an immediate timer is queued
from inside an executing callback, that timer will not be triggered until the
next event loop iteration.
If callback is not a function, a TypeError will be thrown.
This method has a custom variant for promises that is available using
timersPromises.setImmediate().
setInterval(callback[, delay[, ...args]])#
callback <Function> The function to call when the timer elapses.
delay <number> The number of milliseconds to wait before calling the
callback. Default: 1.
...args <any> Optional arguments to pass when the callback is called.
- Returns: <Timeout> for use with
clearInterval()
Schedules repeated execution of callback every delay milliseconds.
When delay is larger than 2147483647 or less than 1, the delay will be
set to 1. Non-integer delays are truncated to an integer.
If callback is not a function, a TypeError will be thrown.
This method has a custom variant for promises that is available using
timersPromises.setInterval().
setTimeout(callback[, delay[, ...args]])#
callback <Function> The function to call when the timer elapses.
delay <number> The number of milliseconds to wait before calling the
callback. Default: 1.
...args <any> Optional arguments to pass when the callback is called.
- Returns: <Timeout> for use with
clearTimeout()
Schedules execution of a one-time callback after delay milliseconds.
The callback will likely not be invoked in precisely delay milliseconds.
Node.js makes no guarantees about the exact timing of when callbacks will fire,
nor of their ordering. The callback will be called as close as possible to the
time specified.
When delay is larger than 2147483647 or less than 1, the delay
will be set to 1. Non-integer delays are truncated to an integer.
If callback is not a function, a TypeError will be thrown.
This method has a custom variant for promises that is available using
timersPromises.setTimeout().
Cancelling timers#
The setImmediate(), setInterval(), and setTimeout() methods
each return objects that represent the scheduled timers. These can be used to
cancel the timer and prevent it from triggering.
For the promisified variants of setImmediate() and setTimeout(),
an AbortController may be used to cancel the timer. When canceled, the
returned Promises will be rejected with an 'AbortError'.
For setImmediate():
import { setImmediate as setImmediatePromise } from 'node:timers/promises';
const ac = new AbortController();
const signal = ac.signal;
setImmediatePromise('foobar', { signal })
.then(console.log)
.catch((err) => {
if (err.name === 'AbortError')
console.error('The immediate was aborted');
});
ac.abort();const { setImmediate: setImmediatePromise } = require('node:timers/promises');
const ac = new AbortController();
const signal = ac.signal;
setImmediatePromise('foobar', { signal })
.then(console.log)
.catch((err) => {
if (err.name === 'AbortError')
console.error('The immediate was aborted');
});
ac.abort();
For setTimeout():
import { setTimeout as setTimeoutPromise } from 'node:timers/promises';
const ac = new AbortController();
const signal = ac.signal;
setTimeoutPromise(1000, 'foobar', { signal })
.then(console.log)
.catch((err) => {
if (err.name === 'AbortError')
console.error('The timeout was aborted');
});
ac.abort();const { setTimeout: setTimeoutPromise } = require('node:timers/promises');
const ac = new AbortController();
const signal = ac.signal;
setTimeoutPromise(1000, 'foobar', { signal })
.then(console.log)
.catch((err) => {
if (err.name === 'AbortError')
console.error('The timeout was aborted');
});
ac.abort();
clearImmediate(immediate)#
Added in: v0.9.1
Cancels an Immediate object created by setImmediate().
clearInterval(timeout)#
Added in: v0.0.1
Cancels a Timeout object created by setInterval().
clearTimeout(timeout)#
Added in: v0.0.1
Cancels a Timeout object created by setTimeout().
Timers Promises API#
The timers/promises API provides an alternative set of timer functions
that return Promise objects. The API is accessible via
require('node:timers/promises').
import {
setTimeout,
setImmediate,
setInterval,
} from 'node:timers/promises';const {
setTimeout,
setImmediate,
setInterval,
} = require('node:timers/promises');
timersPromises.scheduler.wait(delay[, options])#
Added in: v17.3.0, v16.14.0
delay <number> The number of milliseconds to wait before resolving the
promise.
options <Object>
ref <boolean> Set to false to indicate that the scheduled Timeout
should not require the Node.js event loop to remain active.
Default: true.
signal <AbortSignal> An optional AbortSignal that can be used to
cancel waiting.
- Returns: <Promise>
An experimental API defined by the Scheduling APIs draft specification
being developed as a standard Web Platform API.
Calling timersPromises.scheduler.wait(delay, options) is equivalent
to calling timersPromises.setTimeout(delay, undefined, options).
import { scheduler } from 'node:timers/promises';
await scheduler.wait(1000);
timersPromises.scheduler.yield()#
Added in: v17.3.0, v16.14.0
An experimental API defined by the Scheduling APIs draft specification
being developed as a standard Web Platform API.
Calling timersPromises.scheduler.yield() is equivalent to calling
timersPromises.setImmediate() with no arguments.