Vanilla Javascipt debounce utility

utils-debounce.js

/**
 * Debounce utility based on `underscore` debouce, but simpler
 * usage: `_debounce(onScrollEvent, 100, true)`
 * usually you want atBeginning set to false.
 * use atBeginning if you want `func` is called when teh sequence of calls starts, 
 * instead of waiting until `wait` ms have passed without more calls
 */
window._debounce = window._debounce || function(func, wait, atBeginning) {
  var timeout;
  if (atBeginning){
    return function() {
      var context = this, args = arguments;
      var callNow = !timeout;
      timeout && clearTimeout(timeout);
      timeout = setTimeout(function() {
        timeout = null;
        func.apply(context, args);
      }, wait);
      if (callNow) return func.apply(this, args);
    }
  } else {
    return function() {
      var context = this, args = arguments;
      timeout && clearTimeout(timeout);
      timeout = setTimeout(function() {
        timeout = null;
        func.apply(context, args);
      }, wait);
    }
  }
}