code: function throttle(func, delay) {
        var recent;
        return function throttled() {
          var context = this;
          var args = arguments;
          var now = $mdUtil.now();
  
          if (!recent || (now - recent > delay)) {
            func.apply(context, args);
            recent = now;
          }
        };
      }
docs: Returns a function that can only be triggered every `delay` milliseconds. In other words, the function will not be called unless it has been more than `delay` milliseconds since the last call.