-/*!
- * An interface for scheduling background tasks.
- *
- * Loosely based on https://w3c.github.io/requestidlecallback/
- */
( function ( mw ) {
var maxBusy = 50;
/**
* Schedule a deferred task to run in the background.
*
+ * This allows code to perform tasks in the main thread without impacting
+ * time-critical operations such as animations and response to input events.
+ *
+ * Basic logic is as follows:
+ *
+ * - User input event should be acknowledged within 100ms per [RAIL].
+ * - Idle work should be grouped in blocks of upto 50ms so that enough time
+ * remains for the event handler to execute and any rendering to take place.
+ * - Whenever a native event happens (e.g. user input), the deadline for any
+ * running idle callback drops to 0.
+ * - As long as the deadline is non-zero, other callbacks pending may be
+ * executed in the same idle period.
+ *
+ * See also:
+ *
+ * - <https://developer.mozilla.org/en-US/docs/Web/API/Window/requestIdleCallback>
+ * - <https://w3c.github.io/requestidlecallback/>
+ * - <https://developers.google.com/web/updates/2015/08/using-requestidlecallback>
+ * [RAIL]: https://developers.google.com/web/fundamentals/performance/rail
+ *
* @member mw
* @param {Function} callback
+ * @param {Object} [options]
+ * @param {number} [options.timeout] If set, the callback will be scheduled for
+ * immediate execution after this amount of time (in milliseconds) if it didn't run
+ * by that time.
*/
- mw.requestIdleCallback = mw.requestIdleCallbackInternal;
- /*
- // XXX: Polyfill disabled due to https://bugs.chromium.org/p/chromium/issues/detail?id=647870
- mw.requestIdleCallback = window.requestIdleCallback
- // Bind because it throws TypeError if context is not window
- ? window.requestIdleCallback.bind( window )
- : mw.requestIdleCallbackInternal;
- */
+ mw.requestIdleCallback = window.requestIdleCallback ?
+ window.requestIdleCallback.bind( window ) : // Bind because it throws TypeError if context is not window
+ mw.requestIdleCallbackInternal;
+ // Note: Polyfill was previously disabled due to
+ // https://bugs.chromium.org/p/chromium/issues/detail?id=647870
+ // See also <http://codepen.io/Krinkle/full/XNGEvv>
}( mediaWiki ) );