JavaScript实现移动端元素拖拽功能

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
    #div {
      width: 100%;
      height: 200px;
      background: rosybrown;
    }
    #button {
      position: absolute;
    }
  </style>

</head>

<body>
  <div id="div">
    <button id="button">看我的魔法屌不屌</button>
  </div>
  <script>
    var button = document.getElementById('button')
    button.ontouchstart = function(e) {
      var startX = e.touches[0].clientX - this.offsetLeft;
      var startY = e.touches[0].clientY - this.offsetTop;
      this.ontouchmove = function(e) {
        button.style.left = e.touches[0].clientX - startX + 'px';
        button.style.top = e.touches[0].clientY - startY + 'px';        
      }
    }
    button.ontouchend = function() {
      button.ontouchmove = null;
    }
  </script>
</body>

</html>