window.setImmediate

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This method is used to break up long running operations and run a callback function immediately after the browser has completed other operations such as events and display updates.

Note: This method is not expected to become standard, and is only implemented by recent builds of Internet Explorer and Node.js 0.10+. It meets resistance both from Gecko (Firefox) and Webkit (Google/Apple).

Syntax

var immediateID = setImmediate(func, [param1, param2, ...]);
var immediateID = setImmediate(func);
  • where immediateID is the ID of the immediate which can be used later with window.clearImmediate.
  • func is the function you wish to call.

All parameters will be passed directly to your function.

Notes

The window.clearImmediate method can be used to clear the immediate actions, just like window.clearTimeout for window.setTimeout.

This method can be used instead of the setTimeout(fn, 0) method to execute heavy operations

The feature can be emulated in a few different ways:

  • window.postMessage can be used to trigger an immediate but yielding callback. Do note that Internet Explorer 8 includes a synchronous version of postMessage, which means it cannot be used as a fallback.
  • MessageChannel can be used reliably inside of Web Workers whereas the semantics of postMessage mean it cannot be used there.
  • setTimeout(fn, 0) can  potentially be used, however as it is clamped to 4ms per the HTML spec, it does not make for a suitable polyfill for the natural immediacy of setImmediate.

All of these techniques are incorporated into a robust setImmediate polyfill.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support Not supported Not supported 10 Not supported Not supported
Feature Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support Not supported Not supported Not supported Not supported Not supported

See also

window.clearImmediate

Specification: Efficient Script Yielding

Microsoft setImmediate API Demo

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