lovecoding
/
VIP20


			
				
					
						
						
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							<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    *{
      margin: 0;
      padding: 0;
    }
    #container{
      position: relative;
    }
    #smallBox{
      width: 400px;
      height: 400px;
    }
    #bigBox{
      width: 800px;
      height: 800px;
      left: 400px;
      top: 0;
      position: absolute;
    }
    #drag{
      width: 200px;
      height: 200px;
      background: rgba(0,0,0,0.3);
      position: absolute;
      left: 0;
      top: 0;
      display: none;
    }
  </style>
</head>
<body>
  <div id="container">
    <div id="smallBox">
      <img src="images/1.jpg" alt="">
      <div id="drag"></div>
    </div>
    <div id="bigBox">
      <img src="images/2.jpg" alt="">
    </div>
  </div>
  <script>
    var small = document.getElementById('smallBox')
    var drag = document.getElementById('drag')
    
    //鼠标划入显示遮罩层
    small.onmouseover = function(){
      drag.style.display = 'block'
    }
    //鼠标划出显示遮罩层
    small.onmouseout = function(){
      drag.style.display = 'none'
    }
    //鼠标滑动
    small.onmousemove = function(e){
      var xLeft = e.clientX - drag.offsetWidth / 2
      var xTop = e.clientY - drag.offsetHeight /2

      drag.style.left = xLeft + 'px'
      drag.style.top = xTop + 'px'

      if(drag.offsetLeft <= 0){
        drag.style.left = 0
      }
      if(drag.offsetTop <= 0 ){
        drag.style.top = 0
      }

      //横轴最大移动距离
      var zLeft = small.offsetWidth - drag.offsetWidth
      //纵轴最大移动距离
      var zTop = small.offsetHeight - drag.offsetHeight
      if(drag.offsetLeft > zLeft){
        drag.style.left = zLeft + 'px'
      }
      if(drag.offsetTop > zTop){
        drag.style.top = zTop + 'px'
      }
    }
  </script>
</body>
</html>