添加Javascript触摸事件以拖动div

<div id="myDiv">这是一个可拖动的div。</div>

var myDiv = document.getElementById('myDiv');
var startX, startY;

myDiv.addEventListener('touchstart', function(e) {
    e.preventDefault();
    var touch = e.touches[0];
    startX = touch.clientX - myDiv.offsetLeft;
    startY = touch.clientY - myDiv.offsetTop;
}, false);

myDiv.addEventListener('touchmove', function(e) {
    e.preventDefault();
    var touch = e.touches[0];
    var posX = touch.clientX - startX;
    var posY = touch.clientY - startY;
    myDiv.style.left = posX + 'px';
    myDiv.style.top = posY + 'px';
}, false);

myDiv.addEventListener('touchend', function(e) {
    e.preventDefault();
}, false);