Function to throttle a callback so that it only executes after a specified amount of time has elapsed since the last invocation

throttle.js

function throttle(callback, delay, before) {
  var busy = false;
  var hold = false;

  function callAfterDelay(self, args) {
    setTimeout(function() {
      if (hold) {
        hold = false;
        callAfterDelay(self, args);
        return;
      }

      try {
        callback.apply(self, args);
      } finally {
        busy = false;
      }
    }, delay);
  }

  return function() {
    if (busy) {
      hold = true;
      return;
    }

    if (typeof before === "function") {
      before.apply(this, arguments);
    }

    busy = true;
    callAfterDelay(this, arguments);
  }
}