JavaScript 实现可拖拽弹窗盒子的完整代码与原理

完整代码示例

<!DOCTYPE html>
<html>
<head>
 <title>拖拽盒子</title>
 <style type="text/css">
 *{
 margin:0px;
 padding:0px;
 }
 .dropBox{
 width:300px;
 height:300px;
  top:50%;
  left:50%;
  margin-left: -155px;
  margin-top: -155px;
  display: block;
 border: 5px solid #aaa;
 position: absolute;
 }

 .nav{
 width: 100%;
 height:30px;
 background-color: blue;
 opacity: 0.6;
 }
 .nav a{
 font-size:15px;
 color:white;
 }
 .dropBox .box{
 width:300px;
 height:30px;
 position: absolute;
 left:0px;
 top:0px;
 background-color: darkblue;
 opacity: 0.8;
 cursor:move;
 }
 .close{
 float: right;
 color:white;
 font-size: 15px;
 cursor: pointer;
 }
 .move{
 color:white;
 font-size: 15px;
 }
 </style>
 <script type="text/javascript">
 function $(id){
 return document.getElementById(id);
 }
 window.onload = function(){
 var register = $('register');
 var dropBox = $('dropDiv');
 var box = $('box');
 var box2 = $('box2');
 box2.onclick = function(){
  dropBox.style.display = 'none';
 }
 register.onclick = function(){
  dropBox.style.display = 'block';
 }
  box.onmousedown = function(event){
  var evt = event || window.event;
  var mouseLeft = evt.clientX - dropBox.offsetLeft;
  var mouseTop = evt.clientY - dropBox.offsetTop;
  document.onmousemove = function(event){
  var evt = event || window.event;
  var x = evt.clientX - mouseLeft;
  var y = evt.clientY - mouseTop;
  dropBox.style.left = x + 155 + 'px';
  dropBox.style.top = y + 155 + 'px';
  }
  document.onmouseup = function (){
 document.onmousemove = null;
  }
  }

 }



 </script>
</head>
<body>
 <div class="nav">
 <a href="javascript:void(0);" id="register">点击注册</a>
 </div>
 <div class="dropBox" id="dropDiv">
 <div class="box" id="box">
 <span class="move">注册信息（可以拖拽）</span>
 <span class="close" id="box2">【关闭】</span>
 </div>
 
 </div>
</body>
</html>