JavaScript实现放大镜效果代码示例

2020年04月29日作者：lanshanxiao原文
JavaScript实现放大镜效果：
<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .smallBgImg {
      width: 350px;
      height: 350px;
      border: 1px solid #ccc;
      box-sizing: border-box;
      background-clip: padding-box;
      float: left;
      position: relative;
      cursor: pointer;
    }

    .move {
      border: 1px solid #ccc;
      box-sizing: border-box;
      background: rgba(165, 201, 66, 0.5);
      position: absolute;
      left: 0;
      top: 0;
    }

    .bigBgImg {
      width: 540px;
      height: 540px;
      border: 1px solid #ccc;
      box-sizing: border-box;
      background-clip: padding-box;
      float: left;
      margin-left: 10px;
    }

    .hidden {
      display: none;
    }
  </style>
</head>

<body>
  <div class="smallBgImg">
    <div class="move hidden">

    </div>
  </div>
  <div class="bigBgImg hidden">

  </div>
  <script>
    (function () {
      //基本信息配置
      var config = {
        smallImg: "./image/smallImg.jpg", //小图路径
        smallDom: document.getElementsByClassName("smallBgImg")[0], //小图 dom对象
        bigImg: "./image/bigImg.jpg", //大图路径
        bigDom: document.getElementsByClassName("bigBgImg")[0], //大图 dom对象
        moveDom: document.getElementsByClassName("move")[0], //移动方块的dom对象
        smallSize: { //小图尺寸
          width: 350,
          height: 350
        },
        bigSize: { //大图尺寸
          width: 800,
          height: 800
        },
        divBigSize: { //大图框的尺寸
          width: 540,
          height: 540
        }
      };
      //根据比例尺计算移动框的宽高 移动框/小图尺寸 = 大框尺寸/大图尺寸
      config.moveSize = {
        width: config.divBigSize.width * config.smallSize.width / config.bigSize.width,
        height: config.divBigSize.height * config.smallSize.height / config.bigSize.height
      };
      //小图style的计算值
      config.smallComputedStyle = window.getComputedStyle(config.smallDom);
      //大图style的计算值
      config.bigComputedStyle = window.getComputedStyle(config.bigDom);
      //移动方块style的计算值
      config.moveComputedStyle = window.getComputedStyle(config.moveDom);

      initSmallImg();
      initBigImg();
      initMoveDiv();

      //初始化小图
      function initSmallImg() {
        config.smallDom.style.background = `url("${config.smallImg}") no-repeat left top/contain`; //设置背景图片
        config.smallDom.onmousemove = function (e) { //鼠标移入事件
          //展示移动小块
          config.moveDom.style.display = "block";
          var move = window.getComputedStyle(config.moveDom);
          //获取鼠标在小图中的坐标
          var position = getPosition(e);
          //设置移动框的位置
          setPosition(position);

          //展示大图框
          config.bigDom.style.display = "block";
          //大图框中展示部分大图
          displayBigBgImgSize();
        }

        config.smallDom.onmouseout = function () {
          //移动小块隐藏，大图隐藏
          config.moveDom.style.display = config.bigDom.style.display = "none";
        }
      }

      //初始化大图
      function initBigImg() {
        config.bigDom.style.background = `url("${config.bigImg}") no-repeat`; //设置背景图片
      }

      //初始化移动框
      function initMoveDiv() {
        config.moveDom.style.width = config.moveSize.width + "px";
        config.moveDom.style.height = config.moveSize.height + "px";
      }

      //获取鼠标的坐标位置
      function getPosition(e) {
        if (e.target == config.smallDom) { //若鼠标出现在小图中,事件源是小图
          return { //直接获取鼠标距离事件源的横坐标和纵坐标
            x: e.offsetX,
            y: e.offsetY
          };
        } else { //鼠标出现在移动框中,事件源是移动框
          return {
            x: e.offsetX + parseFloat(config.moveComputedStyle.left) +
              1, //鼠标距离事件源的横坐标 + 事件源在smallDom中的left值 + 边框值
            y: e.offsetY + parseFloat(config.moveComputedStyle.top) +
//鼠标距离事件源的纵坐标 + 事件源在smallDom中的top值 + 边框值
          }
        }
      }

      //设置移动方块的位置
      function setPosition(position) {
        //鼠标要始终在移动方块中央位置
        config.moveDom.style.left = position.x - parseFloat(config.moveComputedStyle.width) / 2 + "px";
        config.moveDom.style.top = position.y - parseFloat(config.moveComputedStyle.height) / 2 + "px";

        //要限制移动框的范围在小图中，否则会超出小图
        var left = parseInt(config.moveComputedStyle.left);
        var top = parseInt(config.moveComputedStyle.top);
        if (left < 0) { //最左
          config.moveDom.style.left = "0px";
        }
        if (left > config.smallSize.width - config.moveSize.width) { //最右
          config.moveDom.style.left = config.smallSize.width - config.moveSize.width + "px";
        }
        if (top < 0) { //最上
          config.moveDom.style.top = "0px";
        }
        if (top > config.smallSize.height - config.moveSize.height) { //最下
          config.moveDom.style.top = config.smallSize.height - config.moveSize.height + "px";
        }
      }

      //展示部分大图
      function displayBigBgImgSize() {

        //移动框的left/小图width = 大图框的left/大图width
        var moveLeft = parseInt(config.moveComputedStyle.left);
        var moveTop = parseInt(config.moveComputedStyle.top);
        config.bigDom.style.backgroundPosition =
          `-${moveLeft*config.bigSize.width/config.smallSize.width}px -${moveTop*config.bigSize.height/config.smallSize.height}px`;
      }
    }());
  </script>
</body>

</html>

index.html
效果展示：
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