Native js implementation magnifying glass

2021-07-22 08:50:38
OfStack

Principle: When the left shadow moves from left to right on the left picture, the right big frame also moves from left to right on the right big picture (although the visual, principle and code are opposite); The so-called enlargement means that an already small picture corresponds to an already large picture.


<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title></title>
  <style>
    *{
      margin:0;
      padding:0;
    }
    .small{
      width: 400px;
      height: 400px;
      position: relative;
      background: url(http://www.qdfuns.com/misc.php?mod=attach&genre=editor&aid=7dca2c442134be6a652e087296c8ac80) no-repeat center;
      border: 1px solid #ccc;
    }
    .small .inner{
      width: 100px;
      height: 100px;
      background: yellow;
      opacity: 0.5;
      filter: alpha(opacity=50);
      position: absolute;
      left:0;
      top:0;
      display: none;
    }
    .big{
      width: 400px;
      height: 400px;
      position: absolute;
      left:410px;
      top:0;
      overflow: hidden;
      border: 1px solid #ccc;
      display: none;
    }
    .big img{
      width: 200%;
      height: 200%;
      position: absolute;
      left:0;
      top:0;
    }
  </style>
</head>
<body>
<div id="small" class="small">
  <div class="inner"></div>
</div>
<div id="big" class="big">
  <img src="http://www.qdfuns.com/misc.php?mod=attach&genre=editor&aid=d7dec5aeff022ea80c47eb76dc5838d8" alt=""/>
</div>
<script>
  var small=document.getElementById('small');
  var inner=small.getElementsByTagName('div')[0];
  var big=document.getElementById('big');
  var img=big.getElementsByTagName('img')[0];
  // When the mouse moves in small When, inner And big Display 
  small.onmouseover=function(){
    big.style.display='block';
    inner.style.display='block';
  };
  // When the mouse is over small When moving: 1 ) Mouse in the inner The middle of  2 ) inner Follow the mouse movement 
  small.onmousemove=function(e){
    e=e||window.event;
    var left=e.clientX-this.offsetLeft-inner.offsetWidth/2;
    var top=e.clientY-this.offsetTop-inner.offsetHeight/2;
    if(left<=0){
      left=0;
    }else if(left>=this.offsetWidth-inner.offsetWidth){
      left=this.offsetWidth-inner.offsetWidth
    }
    if(top<=0){
      top=0;
    }else if(top>=this.offsetHeight-inner.offsetHeight){
      top=this.offsetHeight-inner.offsetHeight
    }
    inner.style.left= left+'px';
    inner.style.top= top+'px';
    // When inner When moving, the big picture follows 1 Start moving, and, big picture and inner Moving in opposite directions; 
    // As the shadow on the left moves from left to right on the picture, the large box on the right moves from left to right on the big picture (although visually the opposite is true). 
    img.style.left=left/(small.offsetWidth-inner.offsetWidth)*(big.offsetWidth-img.offsetWidth)+'px';
    img.style.top=top/(small.offsetHeight-inner.offsetHeight)*(big.offsetHeight-img.offsetHeight)+'px';
  };
  // When the mouse moves away, inner And big Hide; 
  small.onmouseout=function(){
    big.style.display='none';
    inner.style.display='none';
  }
</script>
</body>
</html>