resources/src/startup/mediawiki.requestIdleCallback.js

   1 /* global mw */
   2 mw.requestIdleCallbackInternal = function ( callback ) {
   3         setTimeout( function () {
   4                 var start = mw.now();
   5                 callback( {
   6                         didTimeout: false,
   7                         timeRemaining: function () {
   8                                 // Hard a target maximum busy time of 50 milliseconds
   9                                 return Math.max( 0, 50 - ( mw.now() - start ) );
  10                         }
  11                 } );
  12         }, 1 );
  13 };
  14
  15 /**
  16  * Schedule a deferred task to run in the background.
  17  *
  18  * This allows code to perform tasks in the main thread without impacting
  19  * time-critical operations such as animations and response to input events.
  20  *
  21  * Basic logic is as follows:
  22  *
  23  * - User input event should be acknowledged within 100ms per [RAIL].
  24  * - Idle work should be grouped in blocks of upto 50ms so that enough time
  25  *   remains for the event handler to execute and any rendering to take place.
  26  * - Whenever a native event happens (e.g. user input), the deadline for any
  27  *   running idle callback drops to 0.
  28  * - As long as the deadline is non-zero, other callbacks pending may be
  29  *   executed in the same idle period.
  30  *
  31  * See also:
  32  *
  33  * - <https://developer.mozilla.org/en-US/docs/Web/API/Window/requestIdleCallback>
  34  * - <https://w3c.github.io/requestidlecallback/>
  35  * - <https://developers.google.com/web/updates/2015/08/using-requestidlecallback>
  36  * [RAIL]: https://developers.google.com/web/fundamentals/performance/rail
  37  *
  38  * @member mw
  39  * @param {Function} callback
  40  * @param {Object} [options]
  41  * @param {number} [options.timeout] If set, the callback will be scheduled for
  42  *  immediate execution after this amount of time (in milliseconds) if it didn't run
  43  *  by that time.
  44  */
  45 mw.requestIdleCallback = window.requestIdleCallback ?
  46         // Bind because it throws TypeError if context is not window
  47         window.requestIdleCallback.bind( window ) :
  48         mw.requestIdleCallbackInternal;
  49 // Note: Polyfill was previously disabled due to
  50 // https://bugs.chromium.org/p/chromium/issues/detail?id=647870
  51 // See also <http://codepen.io/Krinkle/full/XNGEvv>