效果：
HTML和CSS部分
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>拖拽demo</title>
<style>
#mydiv{
position: absolute;
top: 0;
left: 0;
100px;
height: 100px;
cursor: pointer;
background-color: #de98f0;
}
</style>
</head>
<body>
<div id="mydiv"></div>
</body>
</html>
Js部分
<script>
var block = document.getElementById("mydiv");
var oW, oH;
block.addEventListener("touchstart", function(e) {
var touches = e.touches[0];
oW = touches.clientX - block.offsetLeft;
oH = touches.clientY - block.offsetTop;
document.addEventListener("touchmove", defaultEvent, false);
}, false)
block.addEventListener("touchmove", function(e) {
var touches = e.touches[0];
var oLeft = touches.clientX - oW;
var oTop = touches.clientY - oH;
if (oLeft < 0) {
oLeft = 0;
} else if (oLeft > document.documentElement.clientWidth - block.offsetWidth) {
oLeft = (document.documentElement.clientWidth - block.offsetWidth);
}
if (oTop < 0) {
oTop = 0;
} else if (oTop > document.documentElement.clientHeight - block.offsetHeight) {
oTop = (document.documentElement.clientHeight - block.offsetHeight);
}
block.style.left = oLeft + "px";
block.style.top = oTop + "px";
}, false);
block.addEventListener("touchend", function() {
document.removeEventListener("touchmove", defaultEvent, false);
}, false);
function defaultEvent(e) {
e.preventDefault();
}
</script>