code: function (fn, delay) {
      var timer = null;
      if (!delay || delay < 16) {
        delay = 16;
      }
  
      return function () {
        var _this = this;
        var args = arguments;
  
        if (timer === null) {
          timer = setTimeout(function () {
            fn.apply(_this, args);
            timer = null;
          }, delay);
        }
      };
    }
docs: 函数节流
  @param fn
  @param delay
  @returns {Function}