前端学习–JS入门(5) 事件监听/事件类型/事件对象

本文介绍: 包含事件触发时相关信息的对象，比如用户按下哪个键、鼠标点击哪个元素。事件类型—触发方式（比如 click/mouse ov e r）当一个函数做参数传递给另一个函数时，这个函数是回调函数。事件是系统运行时发生的动作或者发生的事情。th i s—当前函数运行时所处的环境。事件源–获取被触发的dom元素。事件调用函数–触发了做什么事。mouseenter 鼠标经过。m o use leave 鼠标离开。key down 键盘按下触发。谁调用，th i s 指向谁。click 鼠标点击。focus 获得焦点。

一、事件 监听

事件是系统运行时发生的动作或者发生的事情

1.1 事件 监听

元素对象.addEventListener('事件类型',要执行的函数)

三要素：

事件源–获取被触发的do m元素

事件类型–触发方式（比如 click/m ouseo ver）

事件调用函数–触发了做什么事

案例–随机点名

&lt;!DOCTYPE html&gt;
&lt;html lang="en"&gt;
&lt;head&gt;
    &lt;meta charset="UTF-8"&gt;
    <meta http-equiv="X-UA-Compatible" content="IE=edge"&gt;
    <meta name="viewport" content="width=device-width, initial-scale=1.0"&gt;
    <title&gt;随机</title&gt;
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        .box{
            width: 500px;
            height: 300px;
            margin: 50px auto;
            background-color: rgba(255,192,203,0.4);
            border: 1px dotted #333;
            border-radius: 10px;
        }
        h2{
            margin-top: 20px;
            text-align: center;
        }
        .txt span{
            margin-top: 50px;
            display: inline-block;
            font-size: 18px;
            padding-left: 40px;
        }
        .btn{
            margin-top: 100px;
            margin-left: 250px;
            transform: translate(-50%,0);
        }
        .btn button{
            display: inline-block;
            width: 100px;
            height: 30px;
            margin-right: 20px;
            background-color: deepskyblue;
            font-weight: 600;
            text-align: center;
            line-height: 30px;
            font-size: 18px;
            color: #fff;
            border-radius: 3px;
            border: none;
        }
        .btn button:hover{
            background-color: dodgerblue;
            cursor: pointer;

        }
    </style>
</head>
<body>
    <div class="box">
        <h2>随机点名</h2>
        <div class="txt">
            <span>名字是：</span>
            <span class="name"></span>
        </div>
        <div class="btn">
            <button class="start">开始</button>
            <button class="end">停止</button>
        </div>
    </div>
    <script>
        const arr = ['马超','黄忠','赵云','关羽','张飞','曹操','项羽','程咬金']
        const start = document.querySelector('.start')
        const end = document.querySelector('.end')
        let timeId = 0
        // start.addEventListener('click',function(){
        //     const random = parseInt(Math.random()*arr.length)
        //     const name = document.querySelector('.name')
        //     name.innerHTML = arr[random]
        // })
        start.addEventListener('click',function(){
            timeId = setInterval(function(){
            const random = parseInt(Math.random()*arr.length)
            const name = document.querySelector('.name')
            name.innerHTML = arr[random]
        },200)
        })
        end.addEventListener('click',function(){
            clearInterval(timeId)
        })
    </script>
</body>
</html>

1.2 事件监听 版本

//DOM L0
事件源.on事件 = function(){}

//DOM L2
事件源.addEventListener(事件, 事件处理函数)

//on的方式多次写入被覆盖，add可以绑定多次拥有更多特性

二、事件类型

2.1 鼠标事件

click 鼠标点击

mouseenter 鼠标经过

mouse leave 鼠标离开

终极版轮播图

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8" />
  <meta http-equiv="X-UA-Compatible" content="IE=edge" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <title>轮播图点击切换</title>
  <style>
    * {
      box-sizing: border-box;
    }

    .slider {
      width: 560px;
      height: 400px;
      overflow: hidden;
    }

    .slider-wrapper {
      width: 100%;
      height: 320px;
    }

    .slider-wrapper img {
      width: 100%;
      height: 100%;
      display: block;
      /* transition: all 1s; */
    }

    .slider-footer {
      height: 80px;
      background-color: rgb(100, 67, 68);
      padding: 12px 12px 0 12px;
      position: relative;
    }

    .slider-footer .toggle {
      position: absolute;
      right: 0;
      top: 12px;
      display: flex;
    }

    .slider-footer .toggle button {
      margin-right: 12px;
      width: 28px;
      height: 28px;
      appearance: none;
      border: none;
      background: rgba(255, 255, 255, 0.1);
      color: #fff;
      border-radius: 4px;
      cursor: pointer;
    }

    .slider-footer .toggle button:hover {
      background: rgba(255, 255, 255, 0.2);
    }

    .slider-footer p {
      margin: 0;
      color: #fff;
      font-size: 18px;
      margin-bottom: 10px;
    }

    .slider-indicator {
      margin: 0;
      padding: 0;
      list-style: none;
      display: flex;
      align-items: center;
    }

    .slider-indicator li {
      width: 8px;
      height: 8px;
      margin: 4px;
      border-radius: 50%;
      background: #fff;
      opacity: 0.4;
      cursor: pointer;
    }

    .slider-indicator li.active {
      width: 12px;
      height: 12px;
      opacity: 1;
    }
  </style>
</head>

<body>
  <div class="slider">
    <div class="slider-wrapper">
      <img src="./image/slider01.jpg" alt="" />
    </div>
    <div class="slider-footer">
      <p>对人类来说会不会太超前了？</p>
      <ul class="slider-indicator">
        <li class="active"></li>
        <li></li>
        <li></li>
        <li></li>
        <li></li>
        <li></li>
        <li></li>
        <li></li>
      </ul>
      <div class="toggle">
        <button class="prev">&amp;lt;</button>
        <button class="next">&amp;gt;</button>
      </div>
    </div>
  </div>
  <script>
    // 1. 初始数据
    const sliderData = [
      { url: './image/slider01.jpg', title: '对人类来说会不会太超前了？', color: 'rgb(100, 67, 68)' },
      { url: './image/slider02.jpg', title: '开启剑与雪的黑暗传说！', color: 'rgb(43, 35, 26)' },
      { url: './image/slider03.jpg', title: '真正的jo厨出现了！', color: 'rgb(36, 31, 33)' },
      { url: './image/slider04.jpg', title: '李玉刚：让世界通过B站看到东方大国文化', color: 'rgb(139, 98, 66)' },
      { url: './image/slider05.jpg', title: '快来分享你的寒假日常吧~', color: 'rgb(67, 90, 92)' },
      { url: './image/slider06.jpg', title: '哔哩哔哩小年YEAH', color: 'rgb(166, 131, 143)' },
      { url: './image/slider07.jpg', title: '一站式解决你的电脑配置问题！！！', color: 'rgb(53, 29, 25)' },
      { url: './image/slider08.jpg', title: '谁不想和小猫咪贴贴呢！', color: 'rgb(99, 72, 114)' },
    ]

    const img = document.querySelector('.slider-wrapper img')
    const p = document.querySelector('.slider-footer p')
    const footer = document.querySelector('.slider-footer')
    let i = 0 //控制播放的图片顺序

    //1 右侧按钮业务
    const next = document.querySelector('.next')
    next.addEventListener('click',function(){
      i++
      if(i >= 8)i = 0
      toggle()
    })

    //2 左侧按钮业务
    const prev = document.querySelector('.prev')
    prev.addEventListener('click',function(){
      i--
      if(i < 0)i = i + sliderData.length  
      toggle()
    })

    function toggle(){
      img.src = sliderData[i].url
      p.innerHTML = sliderData[i].title
      footer.style.backgoundColor = sliderData[i].color
      document.querySelector('.slider-indicator .active').classList.remove('active')
      document.querySelector(`.slider-indicator li:nth-child(${i+1})`).classList.add('active')
    }

    //3 自动播放
    let timeId = setInterval(function(){
      //利用js自动调用点击事件
      next.click()
    },2000)

    //4 鼠标经过大盒子 停止定时器 
    const slider = document.querySelector('.slider')
    slider.addEventListener('mouseenter',function(){
      clearInterval(timeId)
    })

    //5 鼠标离开 继续播放
    slider.addEventListener('mouseleave',function(){
      clearInterval(timeId)
      timeId = setInterval(function(){
        //利用js自动调用点击事件
        next.click()
      },2000)
    })
  </script>
</body>

</html>

2.2 焦点事件-表单获得光标

focus 获得焦点

blur 失去焦点

小米搜索框

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        ul {

            list-style: none;
        }

        .mi {
            position: relative;
            width: 223px;
            margin: 100px auto;
        }

        .mi input {
            width: 223px;
            height: 48px;
            padding: 0 10px;
            font-size: 14px;
            line-height: 48px;
            border: 1px solid #e0e0e0;
            outline: none;
        }

        .mi .search {
            border: 1px solid #ff6700;
        }

        .result-list {
            display: none;
            position: absolute;
            left: 0;
            top: 48px;
            width: 223px;
            border: 1px solid #ff6700;
            border-top: 0;
            background: #fff;
        }

        .result-list a {
            display: block;
            padding: 6px 15px;
            font-size: 12px;
            color: #424242;
            text-decoration: none;
        }

        .result-list a:hover {
            background-color: #eee;
        }
    </style>

</head>

<body>
    <div class="mi">
        <input type="search" placeholder="小米笔记本">
        <ul class="result-list">
            <li><a href="#">全部商品</a></li>
            <li><a href="#">小米11</a></li>
            <li><a href="#">小米10S</a></li>
            <li><a href="#">小米笔记本</a></li>
            <li><a href="#">小米手机</a></li>
            <li><a href="#">黑鲨4</a></li>
            <li><a href="#">空调</a></li>
        </ul>
    </div>
    <script>
        const input = document.querySelector('[type=search]')
        const ul = document.querySelector('.result-list')
        input.addEventListener('focus',function(){
            ul.style.display = 'block'
            input.classList.add('search')
        })
        input.addEventListener('blur',function(){
            ul.style.display = 'none'
            input.classList.remove('search')
        })
    </script>
</body>

</html>

2.3 键盘事件

key down 键盘按下触发

key up 键盘抬起触发

2.4 文本事件

input 用户输入触发

const tx = document.querySelector('#tx')
const total = document.querySelector('.total')
tx.addEventListener('focus',function(){
   total.style.opacity = 1
})
tx.addEventListener('blur',function(){
   total.style.opacity = 0
})
tx,addEventListener('input',function(){
    total.innerHTML = `${tx.value.length}/200字`
})

三、事件对象

包含事件触发时相关信息的对象，比如用户按下哪个键、鼠标点击哪个元素

3.1 获取事件对象

//事件绑定的回调函数的第一个参数就是事件对象
//e就是事件对象
元素.addEventListener('click',function(e){

})

3.2 事件对象 常用 属性

type	获取当前的事件类型
clientX/clientY	获取光标相对于浏览器左上角的位置
offsetX/offsetY	获取光标相对于当前DOM元素左上角的位置
key	用户按下键盘键的值

案例–评论 发布

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>评论回车发布</title>
  <style>
    .wrapper {
      min-width: 400px;
      max-width: 800px;
      display: flex;
      justify-content: flex-end;
    }

    .avatar {
      width: 48px;
      height: 48px;
      border-radius: 50%;
      overflow: hidden;
      background: url(./images/avatar.jpg) no-repeat center / cover;
      margin-right: 20px;
    }

    .wrapper textarea {
      outline: none;
      border-color: transparent;
      resize: none;
      background: #f5f5f5;
      border-radius: 4px;
      flex: 1;
      padding: 10px;
      transition: all 0.5s;
      height: 30px;
    }

    .wrapper textarea:focus {
      border-color: #e4e4e4;
      background: #fff;
      height: 50px;
    }

    .wrapper button {
      background: #00aeec;
      color: #fff;
      border: none;
      border-radius: 4px;
      margin-left: 10px;
      width: 70px;
      cursor: pointer;
    }

    .wrapper .total {
      margin-right: 80px;
      color: #999;
      margin-top: 5px;
      opacity: 0;
      transition: all 0.5s;
    }

    .list {
      min-width: 400px;
      max-width: 800px;
      display: flex;
    }

    .list .item {
      width: 100%;
      display: flex;
    }

    .list .item .info {
      flex: 1;
      border-bottom: 1px dashed #e4e4e4;
      padding-bottom: 10px;
    }

    .list .item p {
      margin: 0;
    }

    .list .item .name {
      color: #FB7299;
      font-size: 14px;
      font-weight: bold;
    }

    .list .item .text {
      color: #333;
      padding: 10px 0;
    }

    .list .item .time {
      color: #999;
      font-size: 12px;
    }
  </style>
</head>

<body>
  <div class="wrapper">
    <i class="avatar"></i>
    <textarea id="tx" placeholder="发一条友善的评论" rows="2" maxlength="200"></textarea>
    <button>发布</button>
  </div>
  <div class="wrapper">
    <span class="total">0/200字</span>
  </div>
  <div class="list">
    <div class="item" style="display: none;">
      <i class="avatar"></i>
      <div class="info">
        <p class="name">清风徐来</p>
        <p class="text">大家都辛苦啦，感谢各位大大的努力，能圆满完成真是太好了[笑哭][支持]</p>
        <p class="time">2022-10-10 20:29:21</p>
      </div>
    </div>
  </div>
  <script>
    const tx = document.querySelector('#tx')
    const total = document.querySelector('.total')
    const item = document.querySelector('.item')
    const text = document.querySelector('.text')
    const bt = document.querySelector('.wrapper button')
    tx.addEventListener('focus',function(){
      total.style.opacity = 1
    })
    tx.addEventListener('blur',function(){
      total.style.opacity = 0
    })
    tx,addEventListener('input',function(){
      total.innerHTML = `${tx.value.length}/200字`
    })
    function addComment(){
      //如果用户输入的不是纯空格
      //trim()去除字符串左右的空格
      if(tx.value.trim()!==''){
        item.style.display = 'block'
        text.innerHTML = tx.value
      }
      //清空文本域
      tx.value = ''
      total.innerHTML = `0/200字`
    }

    //按下回车发布评论
    tx.addEventListener('keyup',function(e){
      if(e.key === 'Enter'){
        addComment()
      }
    })
    bt.addEventListener('click',function(){
      addComment()
    })

  </script>
</body>

</html>

四、环境 对象

this–当前函数运行时所处的环境

普通函数中this指向 window

谁调用，this指向谁

五、回调函数

当一个函数做参数传递给另一个函数时，这个函数是回调函数

综合 案例 — tab栏切换

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8" />
  <meta http-equiv="X-UA-Compatible" content="IE=edge" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <title>tab栏切换</title>
  <style>
    * {
      margin: 0;
      padding: 0;
    }

    .tab {
      width: 590px;
      height: 340px;
      margin: 20px;
      border: 1px solid #e4e4e4;
    }

    .tab-nav {
      width: 100%;
      height: 60px;
      line-height: 60px;
      display: flex;
      justify-content: space-between;
    }

    .tab-nav h3 {
      font-size: 24px;
      font-weight: normal;
      margin-left: 20px;
    }

    .tab-nav ul {
      list-style: none;
      display: flex;
      justify-content: flex-end;
    }

    .tab-nav ul li {
      margin: 0 20px;
      font-size: 14px;
    }

    .tab-nav ul li a {
      text-decoration: none;
      border-bottom: 2px solid transparent;
      color: #333;
    }

    .tab-nav ul li a.active {
      border-color: #e1251b;
      color: #e1251b;
    }

    .tab-content {
      padding: 0 16px;
    }

    .tab-content .item {
      display: none;
    }

    .tab-content .item.active {
      display: block;
    }
  </style>
</head>

<body>
  <div class="tab">
    <div class="tab-nav">
      <h3>每日特价</h3>
      <ul>
        <li><a class="active" href="javascript:;">精选</a></li>
        <li><a href="javascript:;">美食</a></li>
        <li><a href="javascript:;">百货</a></li>
        <li><a href="javascript:;">个护</a></li>
        <li><a href="javascript:;">预告</a></li>
      </ul>
    </div>
    <div class="tab-content">
      <div class="item active"><img src="./image/tab00.png" alt="" /></div>
      <div class="item"><img src="./image/tab01.png" alt="" /></div>
      <div class="item"><img src="./image/tab02.png" alt="" /></div>
      <div class="item"><img src="./image/tab03.png" alt="" /></div>
      <div class="item"><img src="./image/tab04.png" alt="" /></div>
    </div>
  </div>
  <script>
    const as = document.querySelectorAll('.tab-nav a')
    for(let i = 0; i < as.length; i++){
      as[i].addEventListener('mouseenter',function() {
        document.querySelector('.tab-nav .active').classList.remove('active')
        this.classList.add('active')

        document.querySelector('.tab-content .active').classList.remove('active')
        document.querySelector(`.tab-content .item:nth-child(${i+1})`).classList.add('active')
      })
    }
  </script>
</body>

</html>