Window: requestIdleCallback() method - Web APIs | MDN * Skip to main content * Skip to search HTML HTML: Markup language HTML reference * Elements * Global attributes * Attributes * See all… HTML guides * Responsive images * HTML cheatsheet * Date & time formats * See all… Markup languages * SVG * MathML * XML CSS CSS: Styling language CSS reference * Properties * Selectors * At-rules * Values * See all… CSS guides * Box model * Animations * Flexbox * Colors * See all… Layout cookbook * Column layouts * Centering an element * Card component * See all… JavaScript JS JavaScript: Scripting language JS reference * Standard built-in objects * Expressions & operators * Statements & declarations * Functions * See all… JS guides * Control flow & error handing * Loops and iteration * Working with objects * Using classes * See all… Web APIs Web APIs: Programming interfaces Web API reference * File system API * Fetch API * Geolocation API * HTML DOM API * Push API * Service worker API * See all… Web API guides * Using the Web animation API * Using the Fetch API * Working with the History API * Using the Web speech API * Using web workers All All web technology Technologies * Accessibility * HTTP * URI * Web extensions * WebAssembly * WebDriver * See all… Topics * Media * Performance * Privacy * Security * Progressive web apps Learn Learn web development Frontend developer course * Getting started modules * Core modules * MDN Curriculum * Check out the video course from Scrimba, our partner Learn HTML * Structuring content with HTML module Learn CSS * CSS styling basics module * CSS layout module Learn JavaScript * Dynamic scripting with JavaScript module Tools Discover our tools * Playground * HTTP Observatory * Border-image generator * Border-radius generator * Box-shadow generator * Color format converter * Color mixer * Shape generator About Get to know MDN better * About MDN * Advertise with us * Community * MDN on GitHub Blog Toggle sidebar * Web * Web APIs * Window * requestIdleCallback() Theme * OS default * Light * Dark English (US) Remember language Learn more * Deutsch * English (US) * Español * Français * 日本語 * 한국어 * Português (do Brasil) * Русский * 中文 (简体) Window: requestIdleCallback() method Limited availability This feature is not Baseline because it does not work in some of the most widely-used browsers. Want more browser support for this feature? Tell us why. * See full compatibility * Learn more 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 thread, 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. Note: A timeout option is strongly recommended for required work, as otherwise it's possible multiple seconds will elapse before the callback is fired. In this article * Syntax * Examples * Specifications * Browser compatibility * See also Syntax js requestIdleCallback(callback) requestIdleCallback(callback, options) 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 an 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 the number of milliseconds represented by this parameter has elapsed and the callback has not already been called, then a task to execute the callback is queued in the event loop (even if doing so risks causing a negative performance impact). timeout must be a positive value or it is ignored. Return value An ID which can be used to cancel the callback by passing it into the window.cancelIdleCallback() method. Examples See our complete example in the article Cooperative Scheduling of Background Tasks API . Specifications Specification requestIdleCallback() # the-requestidlecallback-method Browser compatibility See also * Window.cancelIdleCallback() * IdleDeadline * Window.setTimeout() * Window.setInterval() * Window.requestAnimationFrame() Help improve MDN Yes No Learn how to contribute This page was last modified on Jun 23, 2025 by MDN contributors . 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