506 lines
13 KiB
Markdown
506 lines
13 KiB
Markdown
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## 绑定事件的两种方式/DOM事件的级别
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我们在之前的一篇文章《04-JavaScript/22-DOM简介和DOM操作》中已经讲过事件的概念。这里讲一下绑定（注册）事件的两种方式，我们以onclick事件为例。
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### DOM0的写法：onclick
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```javascript
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element.onclick = function () {
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}
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```
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举例：
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```html
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<body>
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<button>点我</button>
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<script>
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var btn = document.getElementsByTagName("button")[0];
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//这种事件绑定的方法容易被层叠。
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btn.onclick = function () {
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console.log("事件1");
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}
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btn.onclick = function () {
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console.log("事件2");
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}
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</script>
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</body>
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```
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点击按钮后，上方代码的打印结果：
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```html
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事件2
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```
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我们可以看到，这种绑定事件的方式，会层叠掉之前的事件。
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### DOM2的写法：addEventListener
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```javascript
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element.addEventListener('click', function () {
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}, false);
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```
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参数解释：
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- 参数1：事件名(注意，没有on)
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- 参数2：事件名(执行函数)
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- 参数3：**true表示捕获阶段触发，false表示冒泡阶段触发（默认）**。如果不写，则默认为false。【重要】
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举例：
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```html
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<body>
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<button>按钮</button>
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<script>
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var btn = document.getElementsByTagName("button")[0];
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// addEventListener: 事件监听器。 原事件被执行的时候，后面绑定的事件照样被执行
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// 这种写法不会出现层叠。（更适合团队开发）
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btn.addEventListener("click", fn1);
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btn.addEventListener("click", fn2);
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function fn1() {
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console.log("事件1");
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}
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function fn2() {
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console.log("事件2");
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}
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</script>
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</body>
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```
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点击按钮后，上方代码的打印结果：
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```html
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事件1
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事件2
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```
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我们可以看到，这种绑定事件的方式，不会层叠掉之前的事件。
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## 事件对象
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当事件的响应函数被触发时，会产生一个事件对象`event`。浏览器每次都会将这个事件`event`作为实参传进之前的响应函数。
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这个对象中包含了与当前事件相关的一切信息。比如鼠标的坐标、键盘的哪个按键被按下、鼠标滚轮滚动的方向等。
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### 获取 event 对象（兼容性问题）
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所有浏览器都支持event对象，但支持的方式不同。如下。
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（1）普通浏览器的写法是 `event`。比如：
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（2）ie 678 的写法是 `window.event`。此时，事件对象 event 是作为window对象的属性保存的。
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于是，我们可以采取一种兼容性的写法。如下：
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```javascript
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event = event || window.event; // 兼容性写法
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```
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代码举例：
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```html
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<!DOCTYPE html>
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<html>
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<head lang="en">
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<meta charset="UTF-8">
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<title></title>
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</head>
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<body>
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<script>
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//点击页面的任何部分
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document.onclick = function (event) {
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event = event || window.event; ////兼容性写法
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console.log(event);
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console.log(event.timeStamp);
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console.log(event.bubbles);
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console.log(event.button);
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console.log(event.pageX);
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console.log(event.pageY);
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console.log(event.screenX);
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console.log(event.screenY);
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console.log(event.target);
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console.log(event.type);
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console.log(event.clientX);
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console.log(event.clientY);
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}
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</script>
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</body>
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</html>
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```
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### event 属性
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event 有很多属性，比如：
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由于pageX 和 pageY的兼容性不好，我们可以这样做：
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- 鼠标在页面的位置 = 滚动条滚动的距离 + 可视区域的坐标。
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## Event举例
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### 举例1：使 div 跟随鼠标移动
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代码实现：
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```html
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<!DOCTYPE html>
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<html>
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<head>
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<meta charset="UTF-8" />
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<title></title>
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<style type="text/css">
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#box1 {
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width: 100px;
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height: 100px;
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background-color: red;
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/*
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* 开启box1的绝对定位
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*/
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position: absolute;
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}
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</style>
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<script type="text/javascript">
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window.onload = function() {
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/*
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* 使div可以跟随鼠标移动
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*/
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//获取box1
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var box1 = document.getElementById("box1");
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//给整个页面绑定：鼠标移动事件
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document.onmousemove = function(event) {
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//兼容的方式获取event对象
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event = event || window.event;
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// 鼠标在页面的位置 = 滚动条滚动的距离 + 可视区域的坐标。
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var pagex = event.pageX || scroll().left + event.clientX;
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var pagey = event.pageY || scroll().top + event.clientY;
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// 设置div的偏移量（相对于整个页面）
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// 注意，如果想通过 style.left 来设置属性，一定要给 box1开启绝对定位。
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box1.style.left = pagex + "px";
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box1.style.top = pagey + "px";
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};
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};
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// scroll 函数封装
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function scroll() {
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return {
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//此函数的返回值是对象
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left: window.pageYOffset || document.body.scrollTop || document.documentElement.scrollTop,
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right:
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window.pageXOffset || document.body.scrollLeft || document.documentElement.scrollLeft
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};
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}
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</script>
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</head>
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<body style="height: 1000px;width: 2000px;">
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<div id="box1"></div>
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</body>
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</html>
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```
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### 举例2：获取鼠标距离所在盒子的距离
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关键点：
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```
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鼠标距离所在盒子的距离 = 鼠标在整个页面的位置 - 所在盒子在整个页面的位置
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```
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代码演示：
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```html
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<!DOCTYPE html>
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<html>
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<head lang="en">
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<meta charset="UTF-8">
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<title></title>
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<style>
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.box {
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width: 300px;
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height: 200px;
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padding-top: 100px;
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background-color: pink;
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margin: 100px;
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text-align: center;
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font: 18px/30px "simsun";
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cursor: pointer;
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}
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</style>
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</head>
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<body>
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<div class="box">
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</div>
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<script src="animate.js"></script>
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<script>
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//需求：鼠标进入盒子之后只要移动，哪怕1像素，随时显示鼠标在盒子中的坐标。
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//技术点：新事件，onmousemove：在事件源上，哪怕鼠标移动1像素也会触动这个事件。
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//一定程度上，模拟了定时器
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//步骤：
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//1.老三步和新五步
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//2.获取鼠标在整个页面的位置
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//3.获取盒子在整个页面的位置
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//4.用鼠标的位置减去盒子的位置赋值给盒子的内容。
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//1.老三步和新五步
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var div = document.getElementsByTagName("div")[0];
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div.onmousemove = function (event) {
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event = event || window.event;
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//2.获取鼠标在整个页面的位置
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var pagex = event.pageX || scroll().left + event.clientX;
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var pagey = event.pageY || scroll().top + event.clientY;
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//3.获取盒子在整个页面的位置
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// var xx =
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// var yy =
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//4.用鼠标的位置减去盒子的位置赋值给盒子的内容。
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var targetx = pagex - div.offsetLeft;
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var targety = pagey - div.offsetTop;
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this.innerHTML = "鼠标在盒子中的X坐标为：" + targetx + "px;<br>鼠标在盒子中的Y坐标为：" + targety + "px;"
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}
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</script>
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</body>
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</html>
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```
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实现效果：
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### 举例3：商品放大镜
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代码实现：
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（1）index.html:
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```html
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<!DOCTYPE html>
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<html>
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<head lang="en">
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<meta charset="UTF-8">
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<title></title>
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<style>
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* {
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margin: 0;
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padding: 0;
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}
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.box {
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width: 350px;
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height: 350px;
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margin: 100px;
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border: 1px solid #ccc;
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position: relative;
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}
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.big {
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width: 400px;
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height: 400px;
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position: absolute;
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top: 0;
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left: 360px;
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border: 1px solid #ccc;
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overflow: hidden;
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display: none;
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}
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/*mask的中文是：遮罩*/
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.mask {
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width: 175px;
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height: 175px;
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background: rgba(255, 255, 0, 0.4);
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position: absolute;
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top: 0;
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left: 0;
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cursor: move;
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display: none;
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}
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.small {
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position: relative;
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}
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img {
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vertical-align: top;
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}
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</style>
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<script src="tools.js"></script>
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<script>
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window.onload = function () {
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//需求：鼠标放到小盒子上，让大盒子里面的图片和我们同步等比例移动。
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//技术点：onmouseenter==onmouseover 第一个不冒泡
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//技术点：onmouseleave==onmouseout 第一个不冒泡
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//步骤：
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//1.鼠标放上去显示盒子，移开隐藏盒子。
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//2.老三步和新五步（黄盒子跟随移动）
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//3.右侧的大图片，等比例移动。
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//0.获取相关元素
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var box = document.getElementsByClassName("box")[0];
|
|||
|
|
var small = box.firstElementChild || box.firstChild;
|
|||
|
|
var big = box.children[1];
|
|||
|
|
var mask = small.children[1];
|
|||
|
|
var bigImg = big.children[0];
|
|||
|
|
|
|||
|
|
//1.鼠标放上去显示盒子，移开隐藏盒子。(为小盒子绑定事件)
|
|||
|
|
small.onmouseenter = function () {
|
|||
|
|
//封装好方法调用：显示元素
|
|||
|
|
show(mask);
|
|||
|
|
show(big);
|
|||
|
|
}
|
|||
|
|
small.onmouseleave = function () {
|
|||
|
|
//封装好方法调用：隐藏元素
|
|||
|
|
hide(mask);
|
|||
|
|
hide(big);
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
//2.老三步和新五步（黄盒子跟随移动）
|
|||
|
|
//绑定的事件是onmousemove，而事件源是small(只要在小盒子上移动1像素，黄盒子也要跟随)
|
|||
|
|
small.onmousemove = function (event) {
|
|||
|
|
//新五步
|
|||
|
|
event = event || window.event;
|
|||
|
|
|
|||
|
|
//想要移动黄盒子，必须要知道鼠标在small小图中的位置。
|
|||
|
|
var pagex = event.pageX || scroll().left + event.clientX;
|
|||
|
|
var pagey = event.pageY || scroll().top + event.clientY;
|
|||
|
|
|
|||
|
|
//x：mask的left值，y：mask的top值。
|
|||
|
|
var x = pagex - box.offsetLeft - mask.offsetWidth / 2; //除以2，可以保证鼠标mask的中间
|
|||
|
|
var y = pagey - box.offsetTop - mask.offsetHeight / 2;
|
|||
|
|
|
|||
|
|
//限制换盒子的范围
|
|||
|
|
//left取值为大于0，小盒子的宽-mask的宽。
|
|||
|
|
if (x < 0) {
|
|||
|
|
x = 0;
|
|||
|
|
}
|
|||
|
|
if (x > small.offsetWidth - mask.offsetWidth) {
|
|||
|
|
x = small.offsetWidth - mask.offsetWidth;
|
|||
|
|
}
|
|||
|
|
//top同理。
|
|||
|
|
if (y < 0) {
|
|||
|
|
y = 0;
|
|||
|
|
}
|
|||
|
|
if (y > small.offsetHeight - mask.offsetHeight) {
|
|||
|
|
y = small.offsetHeight - mask.offsetHeight;
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
//移动黄盒子
|
|||
|
|
console.log(small.offsetHeight);
|
|||
|
|
mask.style.left = x + "px";
|
|||
|
|
mask.style.top = y + "px";
|
|||
|
|
|
|||
|
|
//3.右侧的大图片，等比例移动。
|
|||
|
|
//如何移动大图片？等比例移动。
|
|||
|
|
// 大图片/大盒子 = 小图片/mask盒子
|
|||
|
|
// 大图片走的距离/mask走的距离 = （大图片-大盒子）/（小图片-黄盒子）
|
|||
|
|
// var bili = (bigImg.offsetWidth-big.offsetWidth)/(small.offsetWidth-mask.offsetWidth);
|
|||
|
|
|
|||
|
|
//大图片走的距离/mask盒子都的距离 = 大图片/小图片
|
|||
|
|
var bili = bigImg.offsetWidth / small.offsetWidth;
|
|||
|
|
|
|||
|
|
var xx = bili * x; //知道比例，就可以移动大图片了
|
|||
|
|
var yy = bili * y;
|
|||
|
|
|
|||
|
|
bigImg.style.marginTop = -yy + "px";
|
|||
|
|
bigImg.style.marginLeft = -xx + "px";
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
</script>
|
|||
|
|
</head>
|
|||
|
|
<body>
|
|||
|
|
<div class="box">
|
|||
|
|
<div class="small">
|
|||
|
|
<img src="images/001.jpg" alt=""/>
|
|||
|
|
<div class="mask"></div>
|
|||
|
|
</div>
|
|||
|
|
<div class="big">
|
|||
|
|
<img src="images/0001.jpg" alt=""/>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
</body>
|
|||
|
|
</html>
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
（2）tools.js:
|
|||
|
|
|
|||
|
|
```javascript
|
|||
|
|
/**
|
|||
|
|
* Created by smyhvae on 2018/02/03.
|
|||
|
|
*/
|
|||
|
|
|
|||
|
|
//显示和隐藏
|
|||
|
|
function show(ele) {
|
|||
|
|
ele.style.display = "block";
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
function hide(ele) {
|
|||
|
|
ele.style.display = "none";
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
function scroll() { // 开始封装自己的scrollTop
|
|||
|
|
if (window.pageYOffset != null) { // ie9+ 高版本浏览器
|
|||
|
|
// 因为 window.pageYOffset 默认的是 0 所以这里需要判断
|
|||
|
|
return {
|
|||
|
|
left: window.pageXOffset,
|
|||
|
|
top: window.pageYOffset
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
else if (document.compatMode === "CSS1Compat") { // 标准浏览器 来判断有没有声明DTD
|
|||
|
|
return {
|
|||
|
|
left: document.documentElement.scrollLeft,
|
|||
|
|
top: document.documentElement.scrollTop
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
return { // 未声明 DTD
|
|||
|
|
left: document.body.scrollLeft,
|
|||
|
|
top: document.body.scrollTop
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
效果演示：
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
## 我的公众号
|
|||
|
|
|
|||
|
|
想学习<font color=#0000ff>**代码之外的技能**</font>？不妨关注我的微信公众号：**千古壹号**（id：`qianguyihao`）。
|
|||
|
|
|
|||
|
|
扫一扫，你将发现另一个全新的世界，而这将是一场美丽的意外：
|
|||
|
|
|
|||
|
|
|