原生Js实现拖拽（适用于pc和移动端）

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>