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doc: general improvements to timers.md
Overall improvements to timers.md documentation, Includes squashed commit from @bengl: doc: add timer classes The timers returned by `setTimeout` and friends are actually instances of `Timeout` and `Immediate`. Documenting them as such, so that the `ref` and `unref` methods can be identified as methods on `Timeout` objects. Sparked by discussion in #5792 PR-URL: #6937 Reviewed-By: Robert Jefe Lindstaedt <robert.lindstaedt@gmail.com> Reviewed-By: Bryan English <bryan@bryanenglish.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
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‎doc/api/globals.md‎

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@@ -208,7 +208,7 @@ but rather than loading the module, just return the resolved filename.
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[native addons]: addons.html
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[timers]: timers.html
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[`clearImmediate`]: timers.html#timers_clearimmediate_immediateobject
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[`clearInterval`]: timers.html#timers_clearinterval_intervalobject
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[`clearInterval`]: timers.html#timers_clearinterval_immediateobject
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[`clearTimeout`]: timers.html#timers_cleartimeout_timeoutobject
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[`setImmediate`]: timers.html#timers_setimmediate_callback_arg
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[`setInterval`]: timers.html#timers_setinterval_callback_delay_arg

‎doc/api/timers.md‎

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Stability: 3 - Locked
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All of the timer functions are globals. You do not need to `require()`
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this module in order to use them.
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The `timer` module exposes a global API for scheduling functions to
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be called at some future period of time. Because the timer functions are
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globals, there is no need to call `require('timers')` to use the API.
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## clearImmediate(immediateObject)
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The timer functions within Node.js implement a similar API as the timers API
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provided by Web Browsers but use a different internal implementation that is
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built around [the Node.js Event Loop][].
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Stops an `immediateObject`, as created by [`setImmediate`][], from triggering.
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## Class: Immediate
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## clearInterval(intervalObject)
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This object is created internally and is returned from [`setImmediate()`][]. It
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can be passed to [`clearImmediate()`][] in order to cancel the scheduled
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actions.
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Stops an `intervalObject`, as created by [`setInterval`][], from triggering.
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## Class: Timeout
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## clearTimeout(timeoutObject)
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This object is created internally and is returned from [`setTimeout()`][] and
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[`setInterval()`][]. It can be passed to [`clearTimeout`][] or
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[`clearInterval()`][] (respectively) in order to cancel the scheduled actions.
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Prevents a `timeoutObject`, as created by [`setTimeout`][], from triggering.
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By default, when a timer is scheduled using either [`setTimeout`] or
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[`setInterval()`][], the Node.js event loop will continue running as long as the
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timer is active. Each of the `Timeout` objects returned by these functions
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export both `timeout.ref()` and `timeout.unref()` functions that can be used to
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control this default behavior.
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## ref()
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### timeout.ref()
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If a timer was previously `unref()`d, then `ref()` can be called to explicitly
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request the timer hold the program open. If the timer is already `ref`d calling
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`ref` again will have no effect.
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When called, requests that the Node.js event loop *not* exit so long as the
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`Timeout` is active. Calling `timeout.ref()` multiple times will have no effect.
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Returns the timer.
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*Note*: By default, all `Timeout` objects are "ref'd", making it normally
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unnecessary to call `timeout.ref()` unless `timeout.unref()` had been called
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previously.
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## setImmediate(callback[, arg][, ...])
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Returns a reference to the `Timeout`.
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Schedules "immediate" execution of `callback` after I/O events'
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callbacks and before timers set by [`setTimeout`][] and [`setInterval`][] are
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triggered. Returns an `immediateObject` for possible use with
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[`clearImmediate`][]. Additional optional arguments may be passed to the
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callback.
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### timeout.unref()
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Callbacks for immediates are queued in the order in which they were created.
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The entire callback queue is processed every event loop iteration. If an
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immediate is queued from inside an executing callback, that immediate won't fire
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until the next event loop iteration.
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When called, the active `Timeout` object will not require the Node.js event loop
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to remain active. If there is no other activity keeping the event loop running,
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the process may exit before the `Timeout` object's callback is invoked. Calling
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`timout.unref()` multiple times will have no effect.
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If `callback` is not a function `setImmediate()` will throw immediately.
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*Note*: Calling `timout.unref()` creates an internal timer that will wake the
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Node.js event loop. Creating too many of these can adversely impact performance
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of the Node.js application.
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## setInterval(callback, delay[, arg][, ...])
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Returns a reference to the `Timeout`.
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## Scheduling Timers
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A timer in Node.js is an internal construct that calls a given function after
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a certain period of time. When a timer's function is called varies depending on
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which method was used to create the timer and what other work the Node.js
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event loop is doing.
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### setImmediate(callback[, ...arg])
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* `callback` {Function} The function to call at the end of this turn of
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[the Node.js Event Loop]
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* `[, ...arg]` Optional arguments to pass when the `callback` is called.
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Schedules the "immediate" execution of the `callback` after I/O events'
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callbacks and before timers created using [`setTimeout()`][] and
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[`setInterval()`][] are triggered. Returns an `Immediate` for use with
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[`clearImmediate()`][].
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When multiple calls to `setImmediate()` are made, the `callback` functions are
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queued for execution in the order in which they are created. The entire callback
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queue is processed every event loop iteration. If an immediate timer is queued
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from inside an executing callback, that timer will not be triggered until the
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next event loop iteration.
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If `callback` is not a function, a [`TypeError`][] will be thrown.
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### setInterval(callback, delay[, ...arg])
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* `callback` {Function} The function to call when the timer elapses.
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* `delay` {number} The number of milliseconds to wait before calling the
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`callback`.
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* `[, ...arg]` Optional arguments to pass when the `callback` is called.
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Schedules repeated execution of `callback` every `delay` milliseconds.
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Returns a `intervalObject` for possible use with [`clearInterval`][]. Additional
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optional arguments may be passed to the callback.
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Returns a `Timeout` for use with [`clearInterval()`][].
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To follow browser behavior, when using delays larger than 2147483647
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milliseconds (approximately 25 days) or less than 1, Node.js will use 1 as the
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`delay`.
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When `delay` is larger than `2147483647` or less than `1`, the `delay` will be
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set to `1`.
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If `callback` is not a function `setInterval()` will throw immediately.
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If `callback` is not a function, a [`TypeError`][] will be thrown.
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## setTimeout(callback, delay[, arg][, ...])
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### setTimeout(callback, delay[, ...arg])
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* `callback` {Function} The function to call when the timer elapses.
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* `delay` {number} The number of milliseconds to wait before calling the
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`callback`.
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* `[, ...arg]` Optional arguments to pass when the `callback` is called.
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Schedules execution of a one-time `callback` after `delay` milliseconds.
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Returns a `timeoutObject` for possible use with [`clearTimeout`][]. Additional
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optional arguments may be passed to the callback.
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Returns a `Timeout` for use with [`clearTimeout()`][].
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The callback will likely not be invoked in precisely `delay` milliseconds.
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The `callback` will likely not be invoked in precisely `delay` milliseconds.
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Node.js makes no guarantees about the exact timing of when callbacks will fire,
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nor of their ordering. The callback will be called as close as possible to the
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time specified.
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To follow browser behavior, when using delays larger than 2147483647
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milliseconds (approximately 25 days) or less than 1, the timeout is executed
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immediately, as if the `delay` was set to 1.
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*Note*: When `delay` is larger than `2147483647` or less than `1`, the `delay`
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will be set to `1`.
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If `callback` is not a function, a [`TypeError`][] will be thrown.
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## Cancelling Timers
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The [`setImmediate()`][], [`setInterval()`][], and [`setTimeout()`][] methods
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each return objects that represent the scheduled timers. These can be used to
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cancel the timer and prevent it from triggering.
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### clearImmediate(immediate)
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* `immediate` {Immediate} An `Immediate` object as returned by
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[`setImmediate()`][].
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Cancels an `Immediate` object created by [`setImmediate()`][].
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### clearInterval(timeout)
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* `timeout` {Timeout} A `Timeout` object as returned by [`setInterval()`][].
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If `callback` is not a function `setTimeout()` will throw immediately.
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Cancels a `Timeout` object created by [`setInterval()`][].
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## unref()
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### clearTimeout(timeout)
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The opaque value returned by [`setTimeout`][] and [`setInterval`][] also has the
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method `timer.unref()` which allows the creation of a timer that is active but
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if it is the only item left in the event loop, it won't keep the program
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running. If the timer is already `unref`d calling `unref` again will have no
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effect.
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* `timeout` {Timeout} A `Timeout` object as returned by [`setTimeout()`][].
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In the case of [`setTimeout`][], `unref` creates a separate timer that will
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wakeup the event loop, creating too many of these may adversely effect event
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loop performance -- use wisely.
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Cancels a `Timeout` object created by [`setTimeout()`][].
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Returns the timer.
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[`clearImmediate`]: timers.html#timers_clearimmediate_immediateobject
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[`clearInterval`]: timers.html#timers_clearinterval_intervalobject
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[`clearTimeout`]: timers.html#timers_cleartimeout_timeoutobject
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[`setImmediate`]: timers.html#timers_setimmediate_callback_arg
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[`setInterval`]: timers.html#timers_setinterval_callback_delay_arg
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[`setTimeout`]: timers.html#timers_settimeout_callback_delay_arg
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[the Node.js Event Loop]: https://github.com/nodejs/node/blob/master/doc/topics/the-event-loop-timers-and-nexttick.md
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[`TypeError`]: errors.html#errors_class_typerror
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[`clearImmediate()`]: timers.html#timers_clearimmediate_immediate
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[`clearInterval()`]: timers.html#timers_clearinterval_timeout
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[`clearTimeout()`]: timers.html#timers_cleartimeout_timeout
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[`setImmediate()`]: timers.html#timers_setimmediate_callback_arg
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[`setInterval()`]: timers.html#timers_setinterval_callback_delay_arg
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[`setTimeout()`]: timers.html#timers_settimeout_callback_delay_arg

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