resources/src/startup/mediawiki.requestIdleCallback.js

   1 /* global mw */
   2 ( function () {
   3         var maxBusy = 50;
   4
   5         mw.requestIdleCallbackInternal = function ( callback ) {
   6                 setTimeout( function () {
   7                         var start = mw.now();
   8                         callback( {
   9                                 didTimeout: false,
  10                                 timeRemaining: function () {
  11                                         return Math.max( 0, maxBusy - ( mw.now() - start ) );
  12                                 }
  13                         } );
  14                 }, 1 );
  15         };
  16
  17         /**
  18          * Schedule a deferred task to run in the background.
  19          *
  20          * This allows code to perform tasks in the main thread without impacting
  21          * time-critical operations such as animations and response to input events.
  22          *
  23          * Basic logic is as follows:
  24          *
  25          * - User input event should be acknowledged within 100ms per [RAIL].
  26          * - Idle work should be grouped in blocks of upto 50ms so that enough time
  27          *   remains for the event handler to execute and any rendering to take place.
  28          * - Whenever a native event happens (e.g. user input), the deadline for any
  29          *   running idle callback drops to 0.
  30          * - As long as the deadline is non-zero, other callbacks pending may be
  31          *   executed in the same idle period.
  32          *
  33          * See also:
  34          *
  35          * - <https://developer.mozilla.org/en-US/docs/Web/API/Window/requestIdleCallback>
  36          * - <https://w3c.github.io/requestidlecallback/>
  37          * - <https://developers.google.com/web/updates/2015/08/using-requestidlecallback>
  38          * [RAIL]: https://developers.google.com/web/fundamentals/performance/rail
  39          *
  40          * @member mw
  41          * @param {Function} callback
  42          * @param {Object} [options]
  43          * @param {number} [options.timeout] If set, the callback will be scheduled for
  44          *  immediate execution after this amount of time (in milliseconds) if it didn't run
  45          *  by that time.
  46          */
  47         mw.requestIdleCallback = window.requestIdleCallback ?
  48                 // Bind because it throws TypeError if context is not window
  49                 window.requestIdleCallback.bind( window ) :
  50                 mw.requestIdleCallbackInternal;
  51         // Note: Polyfill was previously disabled due to
  52         // https://bugs.chromium.org/p/chromium/issues/detail?id=647870
  53         // See also <http://codepen.io/Krinkle/full/XNGEvv>
  54 }() );