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.
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.
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])
#
Added in: v0.9.1
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]])
#
Added in: v0.0.1
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]])
#
Added in: v0.0.1
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()
:
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.log('The immediate was aborted');
});
ac.abort();
For setTimeout()
:
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.log('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 'timers/promises';
const {
setTimeout,
setImmediate,
setInterval,
} = require('node:timers/promises');
timersPromises.setTimeout([delay[, value[, options]]])
#
Added in: v15.0.0
delay
<number> The number of milliseconds to wait before fulfilling the
promise. Default: 1
.
value
<any> A value with which the promise is fulfilled.
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 the scheduled Timeout
.
import {
setTimeout,
} from 'timers/promises';
const res = await setTimeout(100, 'result');
console.log(res);
const {
setTimeout,
} = require('node:timers/promises');
setTimeout(100, 'result').then((res) => {
console.log(res);
});
timersPromises.setImmediate([value[, options]])
#
Added in: v15.0.0
value
<any> A value with which the promise is fulfilled.
options
<Object>
ref
<boolean> Set to false
to indicate that the scheduled Immediate
should not require the Node.js event loop to remain active.
Default: true
.
signal
<AbortSignal> An optional AbortSignal
that can be used to
cancel the scheduled Immediate
.
import {
setImmediate,
} from 'timers/promises';
const res = await setImmediate('result');
console.log(res);
const {
setImmediate,
} = require('node:timers/promises');
setImmediate('result').then((res) => {
console.log(res);
});
timersPromises.setInterval([delay[, value[, options]]])
#
Added in: v15.9.0
Returns an async iterator that generates values in an interval of delay
ms.
delay
<number> The number of milliseconds to wait between iterations.
Default: 1
.
value
<any> A value with which the iterator returns.
options
<Object>
ref
<boolean> Set to false
to indicate that the scheduled Timeout
between iterations should not require the Node.js event loop to
remain active.
Default: true
.
signal
<AbortSignal> An optional AbortSignal
that can be used to
cancel the scheduled Timeout
between operations.
import {
setInterval,
} from 'timers/promises';
const interval = 100;
for await (const startTime of setInterval(interval, Date.now())) {
const now = Date.now();
console.log(now);
if ((now - startTime) > 1000)
break;
}
console.log(Date.now());
const {
setInterval,
} = require('node:timers/promises');
const interval = 100;
(async function() {
for await (const startTime of setInterval(interval, Date.now())) {
const now = Date.now();
console.log(now);
if ((now - startTime) > 1000)
break;
}
console.log(Date.now());
})();
timersPromises.scheduler.wait(delay[, options])
#
Added in: v16.14.0
delay
<number> The number of milliseconds to wait before resolving the
promise.
options
<Object>
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 roughly equivalent
to calling timersPromises.setTimeout(delay, undefined, options)
except that
the ref
option is not supported.
import { scheduler } from 'node:timers/promises';
await scheduler.wait(1000);
timersPromises.scheduler.yield()
#
Added in: 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.