原生JavaScript实现可拖拽弹窗的完整示例与注意事项

完整代码示例

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>弹窗拖拽</title>
  <style>
    *{margin:0;padding:0;}
    .box{position: absolute;width: 400px;height: 300px;top:100px;left:100px;border:1px solid #001c67;background: #}
    .move{position: absolute;width: 100px;height: 100px;top:100px;left:150px;border:1px solid #000;}
    .move:hover{cursor: move;}
    .close{position: absolute;width: 30px;height: 30px;top:0px;right:0px;background:red;text-align: center;line-height: 30px;}
  </style>
  <script>
    window.onload=function(){
      var oMove=document.getElementById('move');
      // 拖曳
      oMove.onmousedown=fnDown;
      // 关闭
      var oClose=document.getElementById('close');
      oClose.onclick=function(){
       document.getElementById('box').style.display='none';
      }
    }
    function fnDown(event){
      event = event || window.event;
      var oDrag=document.getElementById('box'),
        // 光标按下时光标和面板之间的距离
        disX=event.clientX-oDrag.offsetLeft,
        disY=event.clientY-oDrag.offsetTop;
      // 移动
      document.onmousemove=function(event){
        event = event || window.event;
        var l=event.clientX-disX,
          t=event.clientY-disY,
          // 最大left,top值
          leftMax=(document.documentElement.clientWidth || document.body.clientWidth)-oDrag.offsetWidth,
          topMax=(document.documentElement.clientHeight || document.body.clientHeight)-oDrag.offsetHeight;
        if(l<0) l=0;
        if(l>leftMax) l=leftMax;
        if(t<0) t=0;
        if(t>topMax) t=topMax;
        oDrag.style.left=l+'px';
        oDrag.style.top=t+'px';
      }
      // 释放鼠标
      document.onmouseup=function(){
        document.onmousemove=null;
        document.onmouseup=null;
      }
    }
  </script>
</head>
<body>
  <div class="box" id="box">
    <div class="move" id="move">拖拽区域</div>
    <div class="close" id="close">X</div>
  </div>
</body>
</html>