code: function _initPullDown() {
        var _this3 = this;
  
        this.scroll.on('pullingDown', function () {
          _this3.pullDownBefore = false;
          _this3.pullDownNow = true;
  
          _this3.$emit('pullingDown');
  
          _this3.scroll.closePullDown(); // 防止在 bounce 前二次触发
  
        });
        this.scroll.on('scroll', function (pos) {
          if (!_this3.pullDown || pos.y < 0) return;
          var posY = Math.floor(pos.y); // 滚动的y轴位置：Number
  
          if (_this3.pullDownBefore) {
            _this3.bubbleY = Math.max(0, posY + _this3.pullDownInitTop);
            _this3.pullDownStyle = "transform: translateY(".concat(Math.min(posY, -_this3.pullDownInitTop), "px)");
          } else {
            _this3.bubbleY = 0;
          }
  
          if (_this3.isRebounding) {
            _this3.pullDownStyle = "transform: translateY(".concat(Math.min(posY, _this3.pullDownConfig.stop), "px)");
          }
        });
      }
docs: 初始化下拉刷新