devtools/shared/throttle.js

   1 /* This Source Code Form is subject to the terms of the Mozilla Public
   2  * License, v. 2.0. If a copy of the MPL was not distributed with this
   3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   4
   5 "use strict";
   6
   7 // setImmediate is only defined when running in the worker thread
   8 /* globals setImmediate */
   9
  10 /**
  11  * From underscore's `_.throttle`
  12  * http://underscorejs.org
  13  * (c) 2009-2014 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
  14  * Underscore may be freely distributed under the MIT license.
  15  *
  16  * Returns a function, that, when invoked, will only be triggered at most once during a
  17  * given window of time. The throttled function will run as much as it can, without ever
  18  * going more than once per wait duration.
  19  *
  20  * @param  {Function} func
  21  *         The function to throttle
  22  * @param  {number} wait
  23  *         The wait period
  24  * @param  {Object} scope
  25  *         The scope to use for func
  26  * @return {Function} The throttled function
  27  */
  28 function throttle(func, wait, scope) {
  29   let args, result;
  30   let timeout = null;
  31   let previous = 0;
  32
  33   const later = function () {
  34     previous = Date.now();
  35     timeout = null;
  36     result = func.apply(scope, args);
  37     args = null;
  38   };
  39
  40   const throttledFunction = function () {
  41     const now = Date.now();
  42     const remaining = wait - (now - previous);
  43     args = arguments;
  44     if (remaining <= 0) {
  45       if (!isWorker) {
  46         clearTimeout(timeout);
  47       }
  48       timeout = null;
  49       previous = now;
  50       result = func.apply(scope, args);
  51       args = null;
  52     } else if (!timeout) {
  53       // On worker thread, we don't have access to privileged setTimeout/clearTimeout
  54       // API which wouldn't be frozen when the worker is paused. So rely on the privileged
  55       // setImmediate function which executes on the next event loop.
  56       if (isWorker) {
  57         setImmediate(later);
  58         timeout = true;
  59       } else {
  60         timeout = setTimeout(later, remaining);
  61       }
  62     }
  63     return result;
  64   };
  65
  66   function cancel() {
  67     if (timeout) {
  68       if (!isWorker) {
  69         clearTimeout(timeout);
  70       }
  71       timeout = null;
  72     }
  73     previous = 0;
  74     args = undefined;
  75     result = undefined;
  76   }
  77
  78   function flush() {
  79     if (!timeout) {
  80       return result;
  81     }
  82     previous = 0;
  83     return throttledFunction();
  84   }
  85
  86   throttledFunction.cancel = cancel;
  87   throttledFunction.flush = flush;
  88
  89   return throttledFunction;
  90 }
  91
  92 exports.throttle = throttle;