methods: {
        dropMove(el) {
        //    console.log(el)
           for(let i=0; i<this.balls.length; i++) {
               let ball = this.balls[i];
               if(!ball.show) {
                  ball.show = true;
                  ball.el = el;
                  this.dropBalls.push(ball);
                  
 
return;
               }
           }
        },
        beforeEnter(el, done) {
            let count = this.balls.length;
            while (count--) {
                let ball = this.balls[count];
                if(ball.show) {                    
                    let rect = ball.el.getBoundingClientRect();//
 
返回元素的大小及其相對於視口的位置
                    let x = rect.left - 32  //ball-container left:32
                    let y = -(window.innerHeight - rect.top -22);
                    el.style.display = '';
                    el.style.transform = `translate3d(0,${y}px,0)`;//外層元素縱向移動
                    el.style.webkitTransform = `translate3d(0,${y}px,0)`;
                    let inner 
 
= el.getElementsByClassName('inner-hook')[0];//內層元素橫向移動
                    inner.style.webkitTransform = `translate3d(${x}px, 0, 0)`;
                    inner.style.transform = `translate3d(${x}px, 0, 0)`;
                    // console.log(el);
                }
            }
        },
        dropEnter(el, done) {
            /*手動取到offsetHeight, 觸發瀏覽器重繪*/
            let rf = el.offsetHeight;
            this.$nextTick(() => {  //樣式重置回來
                el.style.webkitTransform = 'translate3d(0, 0, 0)'// 設定小球掉落後最終的位置
                el.style.transform = 'translate3d(0, 0, 0)'
                let inner = el.getElementsByClassName('inner-hook')[0]
                inner.style.webkitTransform = 'translate3d(0, 0, 0)'
                inner.style.transform = 'translate3d(0, 0, 0)'
                el.addEventListener('transitionend', done) // Vue為了知道過渡的完成，必須設定相應的事件監聽器。它可以是transitionend或 animationend
            })
            // console.log(el);
        },
        afterEnter(el) {
            let ball = this.dropBalls.shift();
            if(ball) {
                ball.show = false;
                el.style.display = 'none';
            } 
            // console.log(el);
        }