Poptip插件拖动造成IOS下与同页面下mescroll.js也被拖动的解决，即对e.preventDefault();的理解

 1 down() {
 2   this.flags = true;
 3   document.body.addEventListener(‘touchmove‘, function (e) {
 4     e.preventDefault();
 5   }, {passive: false});
 6   var touch;
 7   if (event.touches) {
 8     touch = event.touches[0];
 9   } else {
10     touch = event;
11   }
12   this.position.x = touch.clientX;
13   this.position.y = touch.clientY;
14   this.dx = moveDiv.offsetLeft;
15   this.dy = moveDiv.offsetTop;
16 },

1 // 鼠标释放时候的函数
2 end() {
3   window.localStorage.setItem(‘position‘, JSON.stringify({x: this.xPum, y: this.yPum}));
4   this.flags = false;
5   document.body.addEventListener(‘touchmove‘, function (e) {
6     window.event.returnValue = true;
7   });
8 },