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This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The window.requestIdleCallback() method queues a function to be called during a browser's idle periods. This enables developers to perform background and low priority work on the main event loop, without impacting latency-critical events such as animation and input response. Functions are generally called in first-in-first-out order; however, callbacks which have a timeout specified may be called out-of-order if necessary in order to run them before the timeout elapses.

You can call requestIdleCallback() within an idle callback function to schedule another callback to take place no sooner than the next pass through the event loop.

A timeout option is strongly recommended for required work, as otherwise it's possible multiple seconds will elapse before the callback is fired.

Syntax

var handle = window.requestIdleCallback(callback[, options])

Return value

An ID which can be used to cancel the callback by passing it into the window.cancelIdleCallback() method.

Parameters

callback
A reference to a function that should be called in the near future, when the event loop is idle. The callback function is passed a IdleDeadline object describing the amount of time available and whether or not the callback has been run because the timeout period expired.
options Optional
Contains optional configuration parameters. Currently only one property is defined:
  • timeout: If timeout is specified and has a positive value, and the callback has not already been called by the time timeout milliseconds have passed, the callback will be called during the next idle period, even if doing so risks causing a negative performance impact.

Example

See our complete example in the article Cooperative Scheduling of Background Tasks API.

Specifications

Specification Status Comment
Cooperative Scheduling of Background Tasks Proposed Recommendation Initial definition.

Browser compatibility

Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 47 No support 55 (55) No support 34 No support
Feature Android Webview Chrome for Android Firefox Mobile (Gecko) Firefox OS IE Mobile Opera Mobile Safari Mobile
Basic support 47 47 55.0 (55) No support No support ? No support

requestIdleCallback() is implemented in Firefox 53 but was disabled by default. It is enabled by default starting in Firefox 55.

See also