2019-11-14 21:11:14 +08:00
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## 鼠标的拖拽事件
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拖拽的流程：
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（1）`onmousedown`：当鼠标在被拖拽元素上按下时，开始拖拽；
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（2）`onmousemove`：当鼠标移动时被拖拽元素跟随鼠标移动；
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（3）`onmouseup`：当鼠标松开时，被拖拽元素固定在当前位置。
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## 鼠标的滚轮事件
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`onmousewheel`：鼠标滚轮滚动的事件，会在滚轮滚动时触发。但是火狐不支持该属性。
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`DOMMouseScroll`：在火狐中需要使用 DOMMouseScroll 来绑定滚动事件。注意该事件需要通过addEventListener()函数来绑定。
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## 键盘事件
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### 事件名
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`onkeydown`：按键被按下。
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`onkeyup`：按键被松开。
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**注意**：
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- 如果一直按着某一个按键不松手，那么，`onkeydown`事件会一直触发。此时，松开键盘，`onkeyup`事件会执行一次。
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- 当`onkeydown`连续触发时，第一次和第二次之间会间隔稍微长一点，后续的间隔会非常快。这种设计是为了防止误操作的发生。
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键盘事件一般都会绑定给一些可以获取到焦点的对象或者是document。代码举例：
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```html
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<body>
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<script>
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document.onkeydown = function(event) {
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event = event || window.event;
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console.log('qianguyihao 键盘按下了');
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};
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document.onkeyup = function() {
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console.log('qianguyihao 键盘松开了');
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};
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</script>
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<input type="text" />
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</body>
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```
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### 判断哪个键盘被按下
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可以通过`event`事件对象的`keyCode`来获取按键的编码。
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2019-11-26 19:49:07 +08:00
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此外，`event`事件对象里面还提供了以下几个属性：
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2019-11-14 21:11:14 +08:00
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- altKey
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- ctrlKey
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- shiftKey
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2019-11-26 19:49:07 +08:00
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上面这三个属性，可以用来判断`alt`、`ctrl`、和`shift`是否被按下。如果按下则返回true，否则返回false。代码举例：
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```html
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<body>
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<script>
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document.onkeydown = function(event) {
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event = event || window.event;
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console.log('qianguyihao：键盘按下了');
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// 判断y和ctrl是否同时被按下
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if (event.ctrlKey && event.keyCode === 89) {
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console.log('ctrl和y都被按下了');
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}
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};
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</script>
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</body>
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```
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**举例**：input 文本框中，禁止输入数字。代码实现：
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```html
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<body>
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<input type="text" />
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<script>
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//获取input
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var input = document.getElementsByTagName('input')[0];
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input.onkeydown = function(event) {
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event = event || window.event;
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//console.log('qianguyihao:' + event.keyCode);
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//数字 48 - 57
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//使文本框中不能输入数字
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if (event.keyCode >= 48 && event.keyCode <= 57) {
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//在文本框中输入内容，属于onkeydown的默认行为
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return false; // 如果在onkeydown中取消了默认行为，则输入的内容，不会出现在文本框中
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}
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};
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</script>
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</body>
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```
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2019-11-27 12:05:12 +08:00
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## 举例：通过键盘的方向键，移动盒子
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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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position: absolute;
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}
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</style>
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</head>
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<body>
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<div id="box1"></div>
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<script type="text/javascript">
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// 使div可以根据不同的方向键向不同的方向移动
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/*
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* 按左键，div向左移
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* 按右键，div向右移
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* ...
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*/
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//为document绑定一个按键按下的事件
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document.onkeydown = function(event) {
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event = event || window.event;
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//定义一个变量，来表示移动的速度
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var speed = 10;
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//当用户按了ctrl以后，速度加快
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if (event.ctrlKey) {
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console.log('smyhvae ctrl');
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speed = 20;
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}
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/*
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* 37 左
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* 38 上
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* 39 右
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* 40 下
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*/
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switch (event.keyCode) {
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case 37:
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//alert("向左"); left值减小
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box1.style.left = box1.offsetLeft - speed + 'px'; // 在初始值的基础之上，减去 speed 大小
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break;
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case 39:
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//alert("向右");
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box1.style.left = box1.offsetLeft + speed + 'px';
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break;
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case 38:
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//alert("向上");
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box1.style.top = box1.offsetTop - speed + 'px';
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break;
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case 40:
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//alert("向下");
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box1.style.top = box1.offsetTop + speed + 'px';
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break;
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}
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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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上方代码，待改进的地方：
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（1）移动盒子时，如果要加速，需要先按`方向键`，再按`Ctrl键`。
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（2）首次移动盒子时，动作较慢。后续如果学习了定时器相关的内容，可以再改进。
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2019-11-26 19:49:07 +08:00
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2019-11-14 21:11:14 +08:00
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2019-11-26 19:49:07 +08:00
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## 我的公众号
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2019-11-14 21:11:14 +08:00
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2019-11-26 19:49:07 +08:00
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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`）。
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2019-11-14 21:11:14 +08:00
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2019-11-26 19:49:07 +08:00
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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：
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2019-11-14 21:11:14 +08:00
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2019-11-26 19:49:07 +08:00
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2019-11-14 21:11:14 +08:00
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