resources/src/startup/mediawiki.requestIdleCallback.js

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