javascript实现放大镜功能

Z时代
2024-01-10
分类：IT

本文实例为大家分享了javascript实现放大镜功能的具体代码，供大家参考，具体内容如下

描述：当鼠标在小图片上移动时，通过捕捉鼠标在小图片上的位置, 使放大镜的移动方向与大图的水平和垂直方向相反

如何设计

页面元素

技术要点：事件捕捉和定位

难点：计算

涉及技术

onmouseover：当鼠标指针移动到指定的对象上时发生

onmouseout：鼠标指针移出指定对象时发生

onmousemove：鼠标指针移动时发生

offsetLeft | offsetTop | offsetWidth | offsetHeight

event.clientX | event.clientY

偏移量与style.left

style.left返回字符串，例如30px，而offsetLeft返回数字30。

style.left可以读和写，offsetLeft是只读的。如果我们想改变div的位置，我们可以修改style.left.

style.left应事先定义，否则值为空。

需要考虑

如何使小画面上的放大镜与大图同步移动

IE兼容性问题

代码实现


<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <meta name="viewport" content="width=device-width, initial-scale=1.0">
 <title>Magnifier Effect</title>
 <style>
 *{
  margin: 0;
  padding: 0;
 }
 #wrap{
  width: 400px;
  height: 255px;
  margin: 50px;
  border: 1px solid #ccc;
  display: block;
  position: relative;
 }
 #small-box{
  position: relative;
  z-index: 1;
 }
 #float-box{
  width: 160px;
  height: 120px;
  position: absolute;
  background-color: #ffffcc;
  border:1px solid #ccc;
  filter: alpha(opacity = 50);
  opacity: .5;
  display: none;
 }
 #mask{
  position: absolute;
  display: block;
  width: 400px;
  height: 255px;
  z-index: 10;
  background-color: #ffffff;
  filter: alpha(opacity = 0);
  opacity: 0;
  cursor: move;
 }
 #big-box{
  position: absolute;
  top: 0;
  left: 460px;
  width: 400px;
  height: 300px;
  overflow: hidden;
  border: 1px solid #ccc;
  z-index: 1;
  display: none;
 }
 #big-box img{
  position: absolute;
  z-index: 5; 
 }
 </style>
</head>
<script>
 // 页面加载完毕之后执行
 window.onload = function(){
 // 获取父元素wrap, 小盒子,遮罩层, 放大镜, 大盒子, 大图片
 var wrap = document.getElementById('wrap');
 var smallBox = document.getElementById('small-box');
 var mask = document.getElementById('mask');
 var floatBox = document.getElementById('float-box');
 var bigBox = document.getElementById('big-box');
 var bigImg = bigBox.getElementsByTagName('img')[0];
 console.log(wrap, smallBox, mask, floatBox, bigBox, bigImg); 
 // 鼠标移动到小盒子上时, 放大镜显示, 大盒子显示
 mask.onmouseover = function(){
  floatBox.style.display = 'block';
  bigBox.style.display = 'block';
 }
 // 鼠标移出小盒子时, 放大镜隐藏, 大盒子隐藏
 mask.onmouseout = function(){
  floatBox.style.display = 'none';
  bigBox.style.display = 'none';
 }
 // 添加鼠标移动事件
 mask.onmousemove = function(ev){
  // 获取当前鼠标移动的位置并考虑IE兼容性
  var _event = ev || window.event;
  // 获取放大镜向左移动的距离
  var left = _event.clientX - wrap.offsetLeft - smallBox.offsetLeft - floatBox.offsetWidth / 2;
  var top = _event.clientY - wrap.offsetTop - smallBox.offsetTop - floatBox.offsetHeight / 2;
  // console.log(left, top);
  // 考虑边界情况
  if(left < 0){
  left = 0;
  }else if(left > (mask.offsetWidth - floatBox.offsetWidth)){
  left = mask.offsetWidth - floatBox.offsetWidth;
  }
  if(top < 0){
  top = 0;
  }else if(top > (mask.offsetHeight - floatBox.offsetHeight)){
  top = mask.offsetHeight - floatBox.offsetHeight;
  }
  floatBox.style.left = left + 'px';
  floatBox.style.top = top + 'px';
  // calculate percentage
  var percentX = left / (mask.offsetWidth - floatBox.offsetWidth);
  var percentY = top / (mask.offsetHeight - floatBox.offsetHeight);
  // calculate displacement of big image, big image has opposite direction of magnifying glass
  bigImg.style.left = -percentX * (bigImg.offsetWidth - bigBox.offsetWidth) + 'px';
  bigImg.style.top = -percentY * (bigImg.offsetHeight - bigBox.offsetHeight) + 'px';
 }
 }
</script>
<body>
 <div id="wrap">
 <div id="small-box">
  <div id="mask"></div>
  <div id="float-box"></div>
  <img src="./img/macbook-small.jpg" alt="smallMac">
 </div>
 <div id="big-box">
  <img src="./img/macbook-big.jpg" alt="bigMac">
 </div>
 </div>
</body>
</html>