# Timers

    Stability: 3 - Locked

All of the timer functions are globals.  You do not need to `require()`
this module in order to use them.

## clearImmediate(immediateObject)

Stops an immediate from triggering.

## clearInterval(intervalObject)

Stops an interval from triggering.

## clearTimeout(timeoutObject)

Prevents a timeout from triggering.

## ref()

If you had previously `unref()`d a timer you can call `ref()` to explicitly
request the timer hold the program open. If the timer is already `ref`d calling
`ref` again will have no effect.

Returns the timer.

## setImmediate(callback[, arg][, ...])

To schedule the "immediate" execution of `callback` after I/O events
callbacks and before [`setTimeout`][] and [`setInterval`][]. Returns an
`immediateObject` for possible use with `clearImmediate()`. Optionally you
can also pass arguments to the callback.

Callbacks for immediates are queued in the order in which they were created.
The entire callback queue is processed every event loop iteration. If you queue
an immediate from inside an executing callback, that immediate won't fire
until the next event loop iteration.

## setInterval(callback, delay[, arg][, ...])

To schedule the repeated execution of `callback` every `delay` milliseconds.
Returns a `intervalObject` for possible use with `clearInterval()`. Optionally
you can also pass arguments to the callback.

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`.

## setTimeout(callback, delay[, arg][, ...])

To schedule execution of a one-time `callback` after `delay` milliseconds.
Returns a `timeoutObject` for possible use with `clearTimeout()`. Optionally you
can also pass arguments to the callback.

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.

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.

## unref()

The opaque value returned by [`setTimeout`][] and [`setInterval`][] also has the
method `timer.unref()` which will allow you to create 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.

In the case of `setTimeout` when you `unref` you create a separate timer that
will wakeup the event loop, creating too many of these may adversely effect
event loop performance -- use wisely.

Returns the timer.

[`setInterval`]: timers.html#timers_setinterval_callback_delay_arg
[`setTimeout`]: timers.html#timers_settimeout_callback_delay_arg
