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# Timers
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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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## setTimeout(callback, delay[, arg][, ...])
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To schedule execution of a one-time `callback` after `delay` milliseconds. Returns a
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`timeoutObject` for possible use with `clearTimeout()`. Optionally you can
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also pass arguments to the callback.
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It is important to note that your callback will probably not be called in exactly
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`delay` milliseconds - node.js makes no guarantees about the exact timing of when
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the callback will fire, nor of the ordering things will fire in. The callback will
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be called as close as possible to the time specified.
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## clearTimeout(timeoutObject)
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Prevents a timeout from triggering.
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## setInterval(callback, delay[, arg][, ...])
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To schedule the repeated execution of `callback` every `delay` milliseconds.
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Returns a `intervalObject` for possible use with `clearInterval()`. Optionally
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you can also pass arguments to the callback.
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## clearInterval(intervalObject)
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Stops an interval from triggering.
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## unref()
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The opaque value returned by `setTimeout` and `setInterval` also has the method
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`timer.unref()` which will allow you to create a timer that is active but if
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it is the only item left in the event loop, it won't keep the program running.
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If the timer is already `unref`d calling `unref` again will have no effect.
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In the case of `setTimeout` when you `unref` you create a separate timer that
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will wakeup the event loop, creating too many of these may adversely effect
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event loop performance -- use wisely.
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## ref()
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If you had previously `unref()`d a timer you can call `ref()` 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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## setImmediate(callback[, arg][, ...])
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To schedule the "immediate" execution of `callback` after I/O events
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callbacks and before `setTimeout` and `setInterval` . Returns an
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`immediateObject` for possible use with `clearImmediate()`. Optionally you
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can also pass arguments to the callback.
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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 you queue
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an immediate from inside an executing callback, that immediate won't fire
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until the next event loop iteration.
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## clearImmediate(immediateObject)
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Stops an immediate from triggering.
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