js模拟实现京东详情页图片放大效果

<div class="preview_img"> <img src="upload/s3.png" alt=""> <div class="mask"></div> <div class="big">  <img src="upload/big.jpg" alt="" class="bigImg"> </div></div>

.preview_img { position: relative; height: 398px; border: 1px solid #ccc;}.mask { display: none; position: absolute; width: 300px; height: 300px; top: 0; left: 0; background: #FEFE4F; opacity: .5; border: 1px solid #ccc; cursor: move;}.big { display: none; position: absolute; width: 550px; height: 550px; top: 0; left: 410px; z-index: 999; border: 1px solid #ccc; overflow: hidden;}.big img { position: absolute; left: 0; top: 0;}

window.addEventListener('load',function(){    var preview_img = document.querySelector('.preview_img');    var mask = this.document.querySelector('.mask');    var big = this.document.querySelector('.big');    var bigImg = this.document.querySelector('.bigImg');    //鼠标经过    preview_img.addEventListener('mouseover',function(){        mask.style.display = 'block';        big.style.display = 'block';    })    //鼠标移出去    preview_img.addEventListener('mouseout',function(){        mask.style.display = 'none';        big.style.display = 'none';    })    //鼠标移动的时候    preview_img.addEventListener('mousemove',function(e){        //鼠标在盒子内的坐标        var x = e.pageX - this.offsetLeft;        var y = e.pageY - this.offsetTop;        //遮挡层移动的距离        var maskX = x - mask.offsetWidth/2;        var maskY = y -mask.offsetHeight/2;        //大图移动距离        //遮挡层的最大移动距离        var maskMaxX = preview_img.offsetWidth - mask.offsetWidth;        var maskMaxY = preview_img.offsetHeight - mask.offsetHeight;        //如果X坐标小于0  就让它停留在0 的位置        if (maskX <= 0) {            maskX = 0;        }else if (maskX >= maskMaxX) {            maskX = maskMaxX;        }        //如果Y坐标小于0  就让它停留在0 的位置        if (maskY <= 0) {            maskY = 0;        }else if (maskY >= maskMaxY) {            maskY = maskMaxY;        }        //遮挡层移动        mask.style.left = maskX + 'px';        mask.style.top = maskY + 'px';                //大图片最大移动距离        var bigMaxX = bigImg.offsetWidth - big.offsetWidth;        var bigMaxY = bigImg.offsetHeight - big.offsetHeight;        //大图片的移动距离 X Y        // 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 bigX = maskX * bigMaxX / maskMaxX;        var bigY = maskY * bigMaxY / maskMaxY;        //大图和小图（鼠标移动）方向相反        bigImg.style.left = -bigX + 'px';        bigImg.style.top = -bigY + 'px';    })})