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Stability: 3 - Locked
All of the timer functions are globals. You do not need to `require()`
this module in order to use them.
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('timers')` to use the API.
## clearImmediate(immediateObject)
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][].
Stops an `immediateObject` , as created by [`setImmediate`][], from triggering.
## Class: Immediate
## clearInterval(intervalObject)
This object is created internally and is returned from [`setImmediate()`][]. It
can be passed to [`clearImmediate()`][] in order to cancel the scheduled
actions.
Stops an `intervalObject` , as created by [`setInterval`][], from triggering.
## Class: Timeout
## clearTimeout(timeoutObject)
This object is created internally and is returned from [`setTimeout()`][] and
[`setInterval()`][]. It can be passed to [`clearTimeout`][] or
[`clearInterval()`][] (respectively) in order to cancel the scheduled actions.
Prevents a `timeoutObject` , as created by [`setTimeout`][], from triggering.
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.
## ref()
### timeout. ref()
If a timer was previously `unref()` d, then `ref()` can be called to explicitly
request the timer hold the program open. If the timer is already `ref` d calling
`ref` again will have no effect.
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.
Returns the timer.
*Note*: By default, all `Timeout` objects are "ref'd", making it normally
unnecessary to call `timeout.ref()` unless `timeout.unref()` had been called
previously.
## setImmediate(callback[, arg][, ...])
Returns a reference to the `Timeout` .
Schedules "immediate" execution of `callback` after I/O events'
callbacks and before timers set by [`setTimeout`][] and [`setInterval`][] are
triggered. Returns an `immediateObject` for possible use with
[`clearImmediate`][]. Additional optional arguments may be passed to the
callback.
### timeout.unref()
Callbacks for immediates are queued in the order in which they were created.
The entire callback queue is processed every event loop iteration. If an
immediate is queued from inside an executing callback, that immediate won't fire
until the next event loop iteration .
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
`timout.unref()` multiple times will have no effect
If `callback` is not a function `setImmediate()` will throw immediately.
*Note*: Calling `timout.unref()` creates an internal timer that will wake the
Node.js event loop. Creating too many of these can adversely impact performance
of the Node.js application.
## setInterval(callback, delay[, arg][, ...])
Returns a reference to 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[, ...arg])
* `callback` {Function} The function to call at the end of this turn of
[the Node.js Event Loop]
* `[, ...arg]` Optional arguments to pass when the `callback` is called.
Schedules the "immediate" execution of the `callback` after I/O events'
callbacks and before timers created using [`setTimeout()`][] and
[`setInterval()`][] are triggered. Returns an `Immediate` for use with
[`clearImmediate()`][].
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.
### setInterval(callback, delay[, ...arg])
* `callback` {Function} The function to call when the timer elapses.
* `delay` {number} The number of milliseconds to wait before calling the
`callback` .
* `[, ...arg]` Optional arguments to pass when the `callback` is called.
Schedules repeated execution of `callback` every `delay` milliseconds.
Returns a `intervalObject` for possible use with [`clearInterval`][]. Additional
optional arguments may be passed to the callback.
Returns a `Timeout` for use with [`clearInterval()`][].
To follow browser behavior, when using delays larger than 2147483647
milliseconds (approximately 25 days) or less than 1, Node.js will use 1 as the
`delay` .
When `delay` is larger than `2147483647` or less than `1` , the `delay` will be
set to `1` .
If `callback` is not a function `setInterval()` will throw immediately.
If `callback` is not a function, a [`TypeError`][] will be thrown .
## setTimeout(callback, delay[, arg][, ...])
### setTimeout(callback, delay[, ...arg])
* `callback` {Function} The function to call when the timer elapses.
* `delay` {number} The number of milliseconds to wait before calling the
`callback` .
* `[, ...arg]` Optional arguments to pass when the `callback` is called.
Schedules execution of a one-time `callback` after `delay` milliseconds.
Returns a `timeoutObject` for possible use with [`clearTimeout`][]. Additional
optional arguments may be passed to the callback.
Returns a `Timeout` for use with [`clearTimeout()`][].
The callback will likely not be invoked in precisely `delay` milliseconds.
The ` callback` `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.
To follow browser behavior, when using delays larger than 2147483647
milliseconds (approximately 25 days) or less than 1, the timeout is executed
immediately, as if the `delay` was set to 1.
*Note*: When `delay` is larger than `2147483647` or less than `1` , the `delay`
will be set to `1` .
If `callback` is not a function, a [`TypeError`][] will be thrown.
## 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.
### clearImmediate(immediate)
* `immediate` {Immediate} An `Immediate` object as returned by
[`setImmediate()`][].
Cancels an `Immediate` object created by [`setImmediate()`][].
### clearInterval(timeout)
* `timeout` {Timeout} A `Timeout` object as returned by [`setInterval()`][].
If `callback` is not a function `setTimeout()` will throw immediately.
Cancels a `Timeout` object created by [`setInterval()`][] .
## unref()
### clearTimeout(timeout )
The opaque value returned by [`setTimeout`][] and [`setInterval`][] also has the
method `timer.unref()` which allows the creation of a timer that is active but
if it is the only item left in the event loop, it won't keep the program
running. If the timer is already `unref` d calling `unref` again will have no
effect.
* `timeout` {Timeout} A `Timeout` object as returned by [`setTimeout()`][].
In the case of [`setTimeout`][], `unref` creates a separate timer that will
wakeup the event loop, creating too many of these may adversely effect event
loop performance -- use wisely.
Cancels a `Timeout` object created by [`setTimeout()`][].
Returns the timer.
[`clearImmediate`]: timers.html#timers_clearimmediate_immediateobject
[`clearInterval`]: timers.html#timers_clearinterval_intervalobject
[`clearTimeout`]: timers.html#timers_cleartimeout_timeoutobject
[`setImmediate`]: timers.html#timers_setimmediate_callback_arg
[`setInterval`]: timers.html#timers_setinterval_callback_delay_arg
[`setTimeout`]: timers.html#timers_settimeout_callback_delay_arg
[the Node.js Event Loop]: https://github.com/nodejs/node/blob/master/doc/topics/the-event-loop-timers-and-nexttick.md
[`TypeError`]: errors.html#errors_class_typerror
[`clearImmediate()`]: timers.html#timers_clearimmediate_immediate
[`clearInterval()`]: timers.html#timers_clearinterval_timeout
[`clearTimeout()`]: timers.html#timers_cleartimeout_timeout
[`setImmediate()`]: timers.html#timers_setimmediate_callback_arg
[`setInterval()`]: timers.html#timers_setinterval_callback_delay_arg
[`setTimeout()`]: timers.html#timers_settimeout_callback_delay_arg
James M Snell
9 years ago