debounce.js

debounce: function(func, wait, immediate) {
  // Returns a function, that, as long as it continues to be invoked, will not
  // be triggered. The function will be called after it stops being called for
  // N milliseconds. If `immediate` is passed, trigger the function on the
  // leading edge, instead of the trailing.
  // taken from https://github.com/jashkenas/underscore/blob/master/underscore.js
  var timeout, args, context, timestamp, result;

  var later = function() {
      var last = new Date().getTime() - timestamp;

      if (last < wait && last >= 0) {
          timeout = setTimeout(later, wait - last);
      } else {
          timeout = null;
          if (!immediate) {
              result = func.apply(context, args);
              if (!timeout) context = args = null;
          }
      }
  };

  return function() {
      context = this;
      args = arguments;
      timestamp = new Date().getTime();
      var callNow = immediate && !timeout;
      if (!timeout) timeout = setTimeout(later, wait);
      if (callNow) {
          result = func.apply(context, args);
          context = args = null;
      }

      return result;
  };
}