JavaScript实现京东风格放大镜效果详解

HTML与CSS结构实现

<style>
      body,
      div {
        margin: 0;
        padding: 0;
      }
      .product {
        position: relative;
        width: 400px;
        height: 400px;
        margin: 50px 0 0 20px;
        border: 1px solid #000;
      }
      .preview_img img {
        width: 300px;
        height: 300px;
        margin: 50px 50px;
      }
      .mask {
        position: absolute;
        display: none;
        top: 20px;
        left: 30px;
        width: 80px;
        height: 80px;
        background-color: yellow;
        opacity: 0.5;
        cursor: move;
      }
      .big {
        position: absolute;
        display: none;
        left: 410px;
        top: 0;
        width: 500px;
        height: 500px;
        z-index: 999;
        overflow: hidden;
      }
      .big img {
        position: absolute;
        top: 0;
        left: 0;
        width: 400px;
        height: 400px;
      }
    </style>
    <!-- 引入js文件 -->
    <script src="detail.js"></script>
  </head>
  <body>
    <div class="product">
      <div class="preview_img">
        <img src="images/xs.jpg" alt="" />
        <div class="mask"></div>
        <div class="big">
          <img src="images/xs.jpg" alt="" class="bigImg" />
        </div>
      </div>
    </div>
</body>

//页面预加载
window.addEventListener("load", function () {
  var preview_img = document.querySelector(".preview_img");
  var mask = document.querySelector(".mask");
  var big = document.querySelector(".big");

  //1.鼠标经过 preview_img 就显示和隐藏 mask 遮挡层 和 big 大盒子
  preview_img.addEventListener("mouseover", function () {
    mask.style.display = "block";
    big.style.display = "block";
  });
  preview_img.addEventListener("mouseout", function () {
    mask.style.display = "none";
    big.style.display = "none";
  });
  //把鼠标坐标给遮挡层是不合适的，因为遮挡层坐标以父盒子为准
  preview_img.addEventListener("mousemove", function (e) {
    //（1）先计算出鼠标在盒子内的坐标
    var x = e.pageX - this.offsetLeft;
    var y = e.pageY - this.offsetTop;
    //（2）减去盒子高度宽度的一半
    //（3）mask 移动的距离
    var maskX = x - mask.offsetWidth / 2;
    var maskY = y - mask.offsetHeight / 2;
    //(4)如果坐标小于0 就让他停在 0 的位置(即超出盒子范围就停止)
    var egdeX = preview_img.offsetWidth - mask.offsetWidth;
    var egdeY = preview_img.offsetHeight - mask.offsetHeight;
    if (maskX <= 0) {
      maskX = 0;
    } else if (maskX >= egdeX) {
      maskX = egdeX;
    }
    if (maskY <= 0) {
      maskY = 0;
    } else if (maskY >= egdeY) {
      maskY = egdeY;
    }
    mask.style.left = maskX + "px";
    mask.style.top = maskY + "px";
    //大图片的移动距离 = 遮挡层移动距离*大图片最大移动距离 / 遮挡层的最大移动距离
    var bigImg = document.querySelector(".bigImg");
    //大图片最大移动距离
    var bigMax = bigImg.offsetWidth - big.offsetWidth;
    //大图片的移动距离 x y
    var bigX = (maskX * bigMax) / egdeX;
    var bigY = (maskY * bigMax) / egdeY;
    bigImg.style.left = -bigX + "px";
    bigImg.style.top = -bigY + "px";
  });
});