js Magnifying Glass It seems that the code can be basically understood, but there is a code that has been tested and I know the effect but I don’t know why it is written like this?
The picture cannot be uploaded, I don’t know why. Then let’s get into the code. Anyone who makes this function should be familiar with it.
<style>
* {margin: 0;padding: 0;}
img {
vertical-align: top;
}
.box {
width: 350px;
height: 350px;
margin:100px;
border: 1px solid #ccc;
position: relative;
}
.big {
width: 450px;
height: 450px;
position: absolute;
top: 0;
left: 360px;
border: 1px solid #ccc;
overflow: hidden;
display: none;
}
.mask {
width: 100px;
height: 100px;
background: rgba(255, 255, 0, 0.4);
position: absolute;
top: 0;
left: 0;
cursor: move;
display: none;
}
.small {
position: relative;
}
.big img {
position: absolute;
top: 0;
left: 0;
}
</style>
</head>
<body>
<p class="box" id="fdj">
<!--小盒子-->
<p class="small">
<img src="images/001.jpg" alt=""/>
<p class="mask"></p>
</p>
<p class="big">
<img src="images/0001.jpg" alt=""/>
</p>
</p>
</body>
</html>
<script>
var fdj = document.getElementById("fdj"); // 获得最大的盒子
var small = fdj.children[0]; // 获得small 小图片 350盒子
var big = fdj.children[1]; // 获得 大图片 800 盒子
var mask = small.children[1]; // 小的黄色盒子
var bigImage = big.children[0]; // 大盒子里面的图片
small.onmouseover = function() { // 鼠标经过显示出他们
mask.style.display = "block";
big.style.display = "block";
};
small.onmouseout = function() {
mask.style.display = "none";
big.style.display = "none";
}
// 鼠标在small 内移动
var x = 0;
var y = 0;
small.onmousemove = function(event) {
var event = event || window.event;
x = event.clientX - this.offsetParent.offsetLeft - mask.offsetWidth /2;// 再某个盒子内的坐标
y = event.clientY - this.offsetParent.offsetTop - mask.offsetHeight /2;
if(x < 0)
{
x = 0;
}
else if(x > small.offsetWidth - mask.offsetWidth)
{
**x = small.offsetWidth - mask.offsetWidth;**
}
if(y<0)
{
y = 0;
}
else if(y > small.offsetHeight - mask.offsetHeight)
{
y = small.offsetHeight - mask.offsetHeight;
}
alert(x);
mask.style.left = x + "px";
mask.style.top = y + "px";
/*计算 ： 夫子 一顿吃 2个馒头 娇子 一顿 4个馒头
问 夫子今天吃了 3个馒头 娇子应该吃几个？ */
/*计算出他们的倍数 4 / 2 2倍
3 * 2 == 6个 */
/* 大图盒子 / 小图盒子 倍数
我们 再小图移动的距离 * 倍数 == 大图的位置*/
bigImage.style.left = -x * big.offsetWidth /small.offsetWidth + "px";
bigImage.style.top = -y * big.offsetHeight /small.offsetHeight + "px";
}Among them, x = small.offsetWidth - mask.offsetWidth. I don't understand this code. Shouldn't both be fixed values? Use alert to test small.offsetWidth - mask.offsetWidth is a fixed value. Testing x is a variable value. Functionally, x should be a variable. But shouldn’t small.offsetWidth and mask.offsetWidth be fixed values?
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
So, this if(){}else if(){} is used for boundary control. The front is the left border, the back is the right border