This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.
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.
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
IdleDeadlineobject describing the amount of time available and whether or not the callback has been run because the timeout period expired. optionsOptional- Contains optional configuration parameters. Currently only one property is defined:
timeout: Iftimeoutis specified and has a positive value, and the callback has not already been called by the time timeout milliseconds have passed, the timeout 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 | Working Draft | Initial definition. |
Browser compatibility
| Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari (WebKit) |
|---|---|---|---|---|---|
| Basic support | 47 | 53 (53) [1] | 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 | 53.0 (53) [1] | ? | ? | ? | ? |
[1] requestIdleCallback() is implemented in Firefox 53 but is disabled by default; to enable it, set the preference dom.requestIdleCallback.enabled to true. It is enabled by default starting in Firefox 55.