VUE指令、computed计算属性和watch 侦听器（附带详细案例）

灰太狼 2024-04-20 12:23 104阅读 0赞

#### 文章目录 ####

*  前言
 *  发现宝藏
 *  一、指令补充
 *   *  1. 指令修饰符
     *  2. v-bind对于样式操作的增强 - class
     *  3. 案例 - 京东秒杀 tab 导航高亮
     *  4. v-bind对于样式操作的增强 - style
     *  5. v-model应用于其他表单元素
 *  二、computed计算属性
 *   *  1. 基础语法
     *  2. 计算属性 vS method 方法
     *  3. 完整写法
     *  4. 成绩案例
 *  三、watch 侦听器
 *   *  1. 基础语法
     *  2. 业务实现
     *  3. 完整写法
 *  四、综合案例:水果购物车
 *   *  1. 渲染
     *  2. 删除和修改数量
     *  3. 全选反选
     *  4. 统计总价
     *  5. 本地持久化
 *  总结

--------------------

## 前言 ##

为了巩固所学的知识，作者尝试着开始发布一些学习笔记类的博客，方便日后回顾。当然，如果能帮到一些萌新进行新技术的学习那也是极好的。作者菜菜一枚，文章中如果有记录错误，欢迎读者朋友们批评指正。

## 发现宝藏 ##

前些天发现了一个巨牛的人工智能学习网站，通俗易懂，风趣幽默，忍不住分享一下给大家。【[宝藏入口][Link 1]】。

## 一、指令补充 ##

### 1. 指令修饰符 ###

![在这里插入图片描述][88c791c2cc384a60b245e986af8fc4cb.png]

*  @keyup.enter

<!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>
    </head>
    <body>
      <div id="app">
        <h3>@keyup.enter  →  监听键盘回车事件</h3>
        <input @keyup.enter="fn" v-model="username" type="text">
      </div>
      <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
      <script>
        const app = new Vue({
          
          el: '#app',
          data: {
          
            username: ''
          },
          methods: {
          
            fn (e) {
          
              // if (e.key === 'Enter') {
          
              //   console.log('键盘回车的时候触发', this.username)
              // }
    
              console.log('键盘回车的时候触发', this.username)
            }
          }
        })
      </script>
    </body>
    </html>

![在这里插入图片描述][87b0a0fad53b4c9e875b7506b66d0e6f.png]

*  .trim .number .stop .prevent

<!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>
        .father {
          
          width: 200px;
          height: 200px;
          background-color: pink;
          margin-top: 20px;
        }
        .son {
          
          width: 100px;
          height: 100px;
          background-color: skyblue;
        }
      </style>
    </head>
    <body>
      <div id="app">
        <h3>v-model修饰符 .trim .number</h3>
        姓名：<input v-model.trim="username" type="text"><br>
        年纪：<input v-model.number="age" type="text"><br>
    
        
        <h3>@事件名.stop     →  阻止冒泡</h3>
        <div @click="fatherFn" class="father">
          <div @click.stop="sonFn" class="son">儿子</div>
        </div>
    
        <h3>@事件名.prevent  →  阻止默认行为</h3>
        <a @click.prevent href="http://www.baidu.com">阻止默认行为</a>
      </div>
      <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
      <script>
        const app = new Vue({
          
          el: '#app',
          data: {
          
            username: '',
            age: '',
          },
          methods: {
          
            fatherFn () {
          
              alert('老父亲被点击了')
            },
            sonFn (e) {
          
              // e.stopPropagation()
              alert('儿子被点击了')
            }
          }
        })
      </script>
    </body>
    </html>

![在这里插入图片描述][0f9b02d2d0a04b839c168ba1265e9de9.png]

### 2. v-bind对于样式操作的增强 - class ###

![在这里插入图片描述][9fd2755924cc485e979ab606d9b9167f.png]

<!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>
        .box {
          
          width: 200px;
          height: 200px;
          border: 3px solid #000;
          font-size: 30px;
          margin-top: 10px;
        }
        .pink {
          
          background-color: pink;
        }
        .big {
          
          width: 300px;
          height: 300px;
        }
      </style>
    </head>
    <body>
    
      <div id="app">
        <div class="box" :class="{ pink: true, big: true }">黑马程序员</div>
        <div class="box" :class="['pink', 'big']">黑马程序员</div>
      </div>
      <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
      <script>
        const app = new Vue({
          
          el: '#app',
          data: {
          
    
          }
        })
      </script>
    </body>
    </html>

![在这里插入图片描述][4fabee23246a42d191fc55f7478bef19.png]

### 3. 案例 - 京东秒杀 tab 导航高亮 ###

![在这里插入图片描述][766a7da22ba74bb3b24591f181a6a394.png]

<!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;
        }
        ul {
          
          display: flex;
          border-bottom: 2px solid #e01222;
          padding: 0 10px;
        }
        li {
          
          width: 100px;
          height: 50px;
          line-height: 50px;
          list-style: none;
          text-align: center;
        }
        li a {
          
          display: block;
          text-decoration: none;
          font-weight: bold;
          color: #333333;
        }
        li a.active {
          
          background-color: #e01222;
          color: #fff;
        }
    
      </style>
    </head>
    <body>
    
      <div id="app">
        <ul>
          <li v-for="(item, index) in list" :key="item.id" @click="activeIndex = index">
            <a :class="{ active: index === activeIndex }" href="#">{
       { item.name }}</a>
          </li>
        </ul>
      </div>
      <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
      <script>
        const app = new Vue({
          
          el: '#app',
          data: {
          
            activeIndex: 2, // 记录高亮
            list: [
              {
           id: 1, name: '京东秒杀' },
              {
           id: 2, name: '每日特价' },
              {
           id: 3, name: '品类秒杀' }
            ]
          }
        })
      </script>
    </body>
    </html>

![在这里插入图片描述][7fe68639fbdd4e95b4385d2302c5abbd.png]

### 4. v-bind对于样式操作的增强 - style ###

![在这里插入图片描述][634f083b73484351aaf837c493d342e9.png]

<!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>
        .progress {
          
          height: 25px;
          width: 400px;
          border-radius: 15px;
          background-color: #272425;
          border: 3px solid #272425;
          box-sizing: border-box;
          margin-bottom: 30px;
        }
        .inner {
          
          width: 50%;
          height: 20px;
          border-radius: 10px;
          text-align: right;
          position: relative;
          background-color: #409eff;
          background-size: 20px 20px;
          box-sizing: border-box;
          transition: all 1s;
        }
        .inner span {
          
          position: absolute;
          right: -20px;
          bottom: -25px;
        }
      </style>
    </head>
    <body>
      <div id="app">
        
        <div class="progress">
          
          <div class="inner" :style="{ width: percent + '%' }">
            <span>{
       { percent }}%</span>
          </div>
        </div>
        <button @click="percent = 25">设置25%</button>
        <button @click="percent = 50">设置50%</button>
        <button @click="percent = 75">设置75%</button>
        <button @click="percent = 100">设置100%</button>
      </div>
      <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
      <script>
        const app = new Vue({
          
          el: '#app',
          data: {
          
            percent: 30
          }
        })
      </script>
    </body>
    </html>

![在这里插入图片描述][d0cfd0d897484e0ebe90fc82f0fed010.png]

### 5. v-model应用于其他表单元素 ###

![在这里插入图片描述][8ed11efc7dcd4b6b90ffa37f919b8f0f.png]

<!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>
        textarea {
          
          display: block;
          width: 240px;
          height: 100px;
          margin: 10px 0;
        }
      </style>
    </head>
    <body>
    
      <div id="app">
        <h3>小黑学习网</h3>
    
        姓名：
          <input type="text" v-model="username"> 
          <br><br>
    
        是否单身：
          <input type="checkbox" v-model="isSingle"> 
          <br><br>
    
        
        性别: 
          <input v-model="gender" type="radio" name="gender" value="1">男
          <input v-model="gender" type="radio" name="gender" value="2">女
          <br><br>
    
        
        所在城市:
          <select v-model="cityId">
            <option value="101">北京</option>
            <option value="102">上海</option>
            <option value="103">成都</option>
            <option value="104">南京</option>
          </select>
          <br><br>
    
        自我描述：
          <textarea v-model="desc"></textarea> 
    
        <button>立即注册</button>
      </div>
      <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
      <script>
        const app = new Vue({
          
          el: '#app',
          data: {
          
            username: '',
            isSingle: false,
            gender: "2",
            cityId: '102',
            desc: ""
          }
        })
      </script>
    </body>
    </html>

![在这里插入图片描述][761b2e0d216c42728e758dece3f880ec.png]

## 二、computed计算属性 ##

### 1. 基础语法 ###

![在这里插入图片描述][107376518cba4ffead181a8c3c23a6b8.png]

<!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>
        table {
          
          border: 1px solid #000;
          text-align: center;
          width: 240px;
        }
        th,td {
          
          border: 1px solid #000;
        }
        h3 {
          
          position: relative;
        }
      </style>
    </head>
    <body>
    
      <div id="app">
        <h3>小黑的礼物清单</h3>
        <table>
          <tr>
            <th>名字</th>
            <th>数量</th>
          </tr>
          <tr v-for="(item, index) in list" :key="item.id">
            <td>{
       { item.name }}</td>
            <td>{
       { item.num }}个</td>
          </tr>
        </table>
    
        
        <p>礼物总数：{
       { totalCount }} 个</p>
      </div>
      <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
      <script>
        const app = new Vue({
          
          el: '#app',
          data: {
          
            // 现有的数据
            list: [
              {
           id: 1, name: '篮球', num: 1 },
              {
           id: 2, name: '玩具', num: 2 },
              {
           id: 3, name: '铅笔', num: 5 },
            ]
          },
          computed: {
          
            totalCount () {
          
              // 基于现有的数据，编写求值逻辑
              // 计算属性函数内部，可以直接通过 this 访问到 app 实例
              // console.log(this.list)
    
              // 需求：对 this.list 数组里面的 num 进行求和 → reduce
              let total = this.list.reduce((sum, item) => sum + item.num, 0)
              return total
            }
          }
        })
      </script>
    </body>
    </html>

![在这里插入图片描述][d8d1908786b744e3998fb50d89ca291b.png]

### 2. 计算属性 vS method 方法 ###

![在这里插入图片描述][a6d087a0514e43baa2151b52c215c0b9.png]

<!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>
        table {
          
          border: 1px solid #000;
          text-align: center;
          width: 300px;
        }
        th,td {
          
          border: 1px solid #000;
        }
        h3 {
          
          position: relative;
        }
        span {
          
          position: absolute;
          left: 145px;
          top: -4px;
          width: 16px;
          height: 16px;
          color: white;
          font-size: 12px;
          text-align: center;
          border-radius: 50%;
          background-color: #e63f32;
        }
      </style>
    </head>
    <body>
    
      <div id="app">
        <h3>小黑的礼物清单?<span>{
       { totalCountFn() }}</span></h3>
        <h3>小黑的礼物清单?<span>{
       { totalCountFn() }}</span></h3>
        <h3>小黑的礼物清单?<span>{
       { totalCountFn() }}</span></h3>
        <h3>小黑的礼物清单?<span>{
       { totalCountFn() }}</span></h3>
        <table>
          <tr>
            <th>名字</th>
            <th>数量</th>
          </tr>
          <tr v-for="(item, index) in list" :key="item.id">
            <td>{
       { item.name }}</td>
            <td>{
       { item.num }}个</td>
          </tr>
        </table>
    
        <p>礼物总数：{
       { totalCountFn() }} 个</p>
      </div>
      <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
      <script>
        const app = new Vue({
          
          el: '#app',
          data: {
          
            // 现有的数据
            list: [
              {
           id: 1, name: '篮球', num: 3 },
              {
           id: 2, name: '玩具', num: 2 },
              {
           id: 3, name: '铅笔', num: 5 },
            ]
          },
    
          methods: {
          
            totalCountFn () {
          
              console.log('methods方法执行了')
              let total = this.list.reduce((sum, item) => sum + item.num, 0)
              return total
            }
          },
    
          computed: {
          
            // 计算属性：有缓存的，一旦计算出来结果，就会立刻缓存
            // 下一次读取 → 直接读缓存就行 → 性能特别高
            // totalCount () {
          
            //   console.log('计算属性执行了')
            //   let total = this.list.reduce((sum, item) => sum + item.num, 0)
            //   return total
            // }
          }
        })
      </script>
    </body>
    </html>

![在这里插入图片描述][f6132ddc17c744d486dbe01e14cc445e.png]

### 3. 完整写法 ###

![在这里插入图片描述][5378acda4f5b4eae841df7e3bd658983.png]

<!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>
        input {
          
          width: 30px;
        }
      </style>
    </head>
    <body>
    
      <div id="app">
        姓：<input type="text" v-model="firstName"> +
        名：<input type="text" v-model="lastName"> =
        <span>{
       { fullName }}</span><br><br>
        
        <button @click="changeName">改名卡</button>
      </div>
      <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
      <script>
        const app = new Vue({
          
          el: '#app',
          data: {
          
            firstName: '刘',
            lastName: '备',
          },
          methods: {
          
            changeName () {
          
              this.fullName = '黄忠'
            }
          },
          computed: {
          
            // 简写 → 获取，没有配置设置的逻辑
            // fullName () {
          
            //   return this.firstName + this.lastName
            // }
    
            // 完整写法 → 获取 + 设置
            fullName: {
          
              // (1) 当fullName计算属性，被获取求值时，执行get（有缓存，优先读缓存）
              //     会将返回值作为，求值的结果
              get () {
          
                return this.firstName + this.lastName
              },
              // (2) 当fullName计算属性，被修改赋值时，执行set
              //     修改的值，传递给set方法的形参
              set (value) {
          
                // console.log(value.slice(0, 1))          
                // console.log(value.slice(1))         
                this.firstName = value.slice(0, 1)
                this.lastName = value.slice(1)
              }
            }
          }
        })
      </script>
    </body>
    </html>

![在这里插入图片描述][ca05f6e1c9404f19a9d1ee271d2c3e0d.png]

### 4. 成绩案例 ###

![在这里插入图片描述][3ced3875890a4bcca4a920c844288b5a.png]

*  渲染实现

<!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" />
        <link rel="stylesheet" href="./styles/index.css" />
        <title>Document</title>
      </head>
      <body>
        <div id="app" class="score-case">
          <div class="table">
            <table>
              <thead>
                <tr>
                  <th>编号</th>
                  <th>科目</th>
                  <th>成绩</th>
                  <th>操作</th>
                </tr>
              </thead>
    
              <tbody v-if="list.length > 0">
                <tr v-for="(item, index) in list" :key="item.id">
                  <td>{
       { index + 1 }}</td>
                  <td>{
       { item.subject }}</td>
                  
                  <td :class="{ red: item.score < 60 }">{
       { item.score }}</td>
                  <td><a href="#">删除</a></td>
                </tr>
              </tbody>
    
              <tbody v-else>
                <tr>
                  <td colspan="5">
                    <span class="none">暂无数据</span>
                  </td>
                </tr>
              </tbody>
    
              <tfoot>
                <tr>
                  <td colspan="5">
                    <span>总分：246</span>
                    <span style="margin-left: 50px">平均分：79</span>
                  </td>
                </tr>
              </tfoot>
            </table>
          </div>
          <div class="form">
            <div class="form-item">
              <div class="label">科目：</div>
              <div class="input">
                <input
                  type="text"
                  placeholder="请输入科目"
                />
              </div>
            </div>
            <div class="form-item">
              <div class="label">分数：</div>
              <div class="input">
                <input
                  type="text"
                  placeholder="请输入分数"
                />
              </div>
            </div>
            <div class="form-item">
              <div class="label"></div>
              <div class="input">
                <button class="submit" >添加</button>
              </div>
            </div>
          </div>
        </div>
        <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
    
        <script>
          const app = new Vue({
          
            el: '#app',
            data: {
          
              list: [
                {
           id: 1, subject: '语文', score: 62 },
                {
           id: 7, subject: '数学', score: 39 },
                {
           id: 12, subject: '英语', score: 70 },
              ],
              subject: '',
              score: ''
            }
          })
        </script>
      </body>
    </html>

*  添加删除

<!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" />
        <link rel="stylesheet" href="./styles/index.css" />
        <title>Document</title>
      </head>
      <body>
        <div id="app" class="score-case">
          <div class="table">
            <table>
              <thead>
                <tr>
                  <th>编号</th>
                  <th>科目</th>
                  <th>成绩</th>
                  <th>操作</th>
                </tr>
              </thead>
    
              <tbody v-if="list.length > 0">
                <tr v-for="(item, index) in list" :key="item.id">
                  <td>{
       { index + 1 }}</td>
                  <td>{
       { item.subject }}</td>
                  
                  <td :class="{ red: item.score < 60 }">{
       { item.score }}</td>
                  <td><a @click.prevent="del(item.id)" href="http://www.baidu.com">删除</a></td>
                </tr>
              </tbody>
    
              <tbody v-else>
                <tr>
                  <td colspan="5">
                    <span class="none">暂无数据</span>
                  </td>
                </tr>
              </tbody>
    
              <tfoot>
                <tr>
                  <td colspan="5">
                    <span>总分：246</span>
                    <span style="margin-left: 50px">平均分：79</span>
                  </td>
                </tr>
              </tfoot>
            </table>
          </div>
          <div class="form">
            <div class="form-item">
              <div class="label">科目：</div>
              <div class="input">
                <input
                  type="text"
                  placeholder="请输入科目"
                  v-model.trim="subject"
                />
              </div>
            </div>
            <div class="form-item">
              <div class="label">分数：</div>
              <div class="input">
                <input
                  type="text"
                  placeholder="请输入分数"
                  v-model.number="score"
                />
              </div>
            </div>
            <div class="form-item">
              <div class="label"></div>
              <div class="input">
                <button @click="add" class="submit" >添加</button>
              </div>
            </div>
          </div>
        </div>
        <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
    
        <script>
          const app = new Vue({
          
            el: '#app',
            data: {
          
              list: [
                {
           id: 1, subject: '语文', score: 62 },
                {
           id: 7, subject: '数学', score: 39 },
                {
           id: 12, subject: '英语', score: 70 },
              ],
              subject: '',
              score: ''
            },
            methods: {
          
              del (id) {
          
                // console.log(id)
                this.list = this.list.filter(item => item.id !== id)
              },
              add () {
          
                if (!this.subject) {
          
                  alert('请输入科目')
                  return
                }
                if (typeof this.score !== 'number') {
          
                  alert('请输入正确的成绩')
                  return
                }
                this.list.unshift({
          
                  id: +new Date(),
                  subject: this.subject,
                  score: this.score
                })
    
                this.subject = ''
                this.score = ''
              }
            }
          })
        </script>
      </body>
    </html>

*  计算属性

<!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" />
        <link rel="stylesheet" href="./styles/index.css" />
        <title>Document</title>
      </head>
      <body>
        <div id="app" class="score-case">
          <div class="table">
            <table>
              <thead>
                <tr>
                  <th>编号</th>
                  <th>科目</th>
                  <th>成绩</th>
                  <th>操作</th>
                </tr>
              </thead>
    
              <tbody v-if="list.length > 0">
                <tr v-for="(item, index) in list" :key="item.id">
                  <td>{
       { index + 1 }}</td>
                  <td>{
       { item.subject }}</td>
                  
                  <td :class="{ red: item.score < 60 }">{
       { item.score }}</td>
                  <td><a @click.prevent="del(item.id)" href="http://www.baidu.com">删除</a></td>
                </tr>
              </tbody>
    
              <tbody v-else>
                <tr>
                  <td colspan="5">
                    <span class="none">暂无数据</span>
                  </td>
                </tr>
              </tbody>
    
              <tfoot>
                <tr>
                  <td colspan="5">
                    <span>总分：{
       { totalScore }}</span>
                    <span style="margin-left: 50px">平均分：{
       { averageScore }}</span>
                  </td>
                </tr>
              </tfoot>
            </table>
          </div>
          <div class="form">
            <div class="form-item">
              <div class="label">科目：</div>
              <div class="input">
                <input
                  type="text"
                  placeholder="请输入科目"
                  v-model.trim="subject"
                />
              </div>
            </div>
            <div class="form-item">
              <div class="label">分数：</div>
              <div class="input">
                <input
                  type="text"
                  placeholder="请输入分数"
                  v-model.number="score"
                />
              </div>
            </div>
            <div class="form-item">
              <div class="label"></div>
              <div class="input">
                <button @click="add" class="submit" >添加</button>
              </div>
            </div>
          </div>
        </div>
        <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
    
        <script>
          const app = new Vue({
          
            el: '#app',
            data: {
          
              list: [
                {
           id: 1, subject: '语文', score: 62 },
                {
           id: 7, subject: '数学', score: 89 },
                {
           id: 12, subject: '英语', score: 70 },
              ],
              subject: '',
              score: ''
            },
            computed: {
          
              totalScore() {
          
                return this.list.reduce((sum, item) => sum + item.score, 0)
              },
              averageScore () {
          
                if (this.list.length === 0) {
          
                  return 0
                }
                return (this.totalScore / this.list.length).toFixed(2)
              }
            },
            methods: {
          
              del (id) {
          
                // console.log(id)
                this.list = this.list.filter(item => item.id !== id)
              },
              add () {
          
                if (!this.subject) {
          
                  alert('请输入科目')
                  return
                }
                if (typeof this.score !== 'number') {
          
                  alert('请输入正确的成绩')
                  return
                }
                this.list.unshift({
          
                  id: +new Date(),
                  subject: this.subject,
                  score: this.score
                })
    
                this.subject = ''
                this.score = ''
              }
            }
          })
        </script>
      </body>
    </html>

![在这里插入图片描述][242a9be1ebf64e72bbaa9cf7cd0256f5.png]  
![在这里插入图片描述][0c5f2187f70b4473bd815207e853ec8c.png]

## 三、watch 侦听器 ##

### 1. 基础语法 ###

![在这里插入图片描述][307e33ed6b5343faab5431205a13fcb1.png]

<!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;
            font-size: 18px;
          }
          #app {
          
            padding: 10px 20px;
          }
          .query {
          
            margin: 10px 0;
          }
          .box {
          
            display: flex;
          }
          textarea {
          
            width: 300px;
            height: 160px;
            font-size: 18px;
            border: 1px solid #dedede;
            outline: none;
            resize: none;
            padding: 10px;
          }
          textarea:hover {
          
            border: 1px solid #1589f5;
          }
          .transbox {
          
            width: 300px;
            height: 160px;
            background-color: #f0f0f0;
            padding: 10px;
            border: none;
          }
          .tip-box {
          
            width: 300px;
            height: 25px;
            line-height: 25px;
            display: flex;
          }
          .tip-box span {
          
            flex: 1;
            text-align: center;
          }
          .query span {
          
            font-size: 18px;
          }
    
          .input-wrap {
          
            position: relative;
          }
          .input-wrap span {
          
            position: absolute;
            right: 15px;
            bottom: 15px;
            font-size: 12px;
          }
          .input-wrap i {
          
            font-size: 20px;
            font-style: normal;
          }
        </style>
      </head>
      <body>
        <div id="app">
          
          <div class="query">
            <span>翻译成的语言：</span>
            <select>
              <option value="italy">意大利</option>
              <option value="english">英语</option>
              <option value="german">德语</option>
            </select>
          </div>
    
          
          <div class="box">
            <div class="input-wrap">
              <textarea v-model="obj.words"></textarea>
              <span><i>⌨️</i>文档翻译</span>
            </div>
            <div class="output-wrap">
              <div class="transbox">mela</div>
            </div>
          </div>
        </div>
        <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
        <script src="https://cdn.jsdelivr.net/npm/axios/dist/axios.min.js"></script>
        <script>
          // 接口地址：https://applet-base-api-t.itheima.net/api/translate
          // 请求方式：get
          // 请求参数：
          // （1）words：需要被翻译的文本（必传）
          // （2）lang： 需要被翻译成的语言（可选）默认值-意大利
          // -----------------------------------------------
          
          const app = new Vue({
          
            el: '#app',
            data: {
          
              // words: ''
              obj: {
          
                words: ''
              }
            },
            // 具体讲解：(1) watch语法 (2) 具体业务实现
            watch: {
          
              // 该方法会在数据变化时调用执行
              // newValue新值, oldValue老值（一般不用）
              // words (newValue) {
          
              //   console.log('变化了', newValue)
              // }
    
              'obj.words' (newValue) {
          
                console.log('变化了', newValue)
              }
            }
          })
        </script>
      </body>
    </html>

![在这里插入图片描述][ae90dcb74d074b07b77af272b975c569.png]

### 2. 业务实现 ###

<!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;
            font-size: 18px;
          }
          #app {
          
            padding: 10px 20px;
          }
          .query {
          
            margin: 10px 0;
          }
          .box {
          
            display: flex;
          }
          textarea {
          
            width: 300px;
            height: 160px;
            font-size: 18px;
            border: 1px solid #dedede;
            outline: none;
            resize: none;
            padding: 10px;
          }
          textarea:hover {
          
            border: 1px solid #1589f5;
          }
          .transbox {
          
            width: 300px;
            height: 160px;
            background-color: #f0f0f0;
            padding: 10px;
            border: none;
          }
          .tip-box {
          
            width: 300px;
            height: 25px;
            line-height: 25px;
            display: flex;
          }
          .tip-box span {
          
            flex: 1;
            text-align: center;
          }
          .query span {
          
            font-size: 18px;
          }
    
          .input-wrap {
          
            position: relative;
          }
          .input-wrap span {
          
            position: absolute;
            right: 15px;
            bottom: 15px;
            font-size: 12px;
          }
          .input-wrap i {
          
            font-size: 20px;
            font-style: normal;
          }
        </style>
      </head>
      <body>
        <div id="app">
          
          <div class="query">
            <span>翻译成的语言：</span>
            <select>
              <option value="italy">意大利</option>
              <option value="english">英语</option>
              <option value="german">德语</option>
            </select>
          </div>
    
          
          <div class="box">
            <div class="input-wrap">
              <textarea v-model="obj.words"></textarea>
              <span><i>⌨️</i>文档翻译</span>
            </div>
            <div class="output-wrap">
              <div class="transbox">{
       { result }}</div>
            </div>
          </div>
        </div>
        <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
        <script src="https://cdn.jsdelivr.net/npm/axios/dist/axios.min.js"></script>
        <script>
          // 接口地址：https://applet-base-api-t.itheima.net/api/translate
          // 请求方式：get
          // 请求参数：
          // （1）words：需要被翻译的文本（必传）
          // （2）lang： 需要被翻译成的语言（可选）默认值-意大利
          // -----------------------------------------------
          
          const app = new Vue({
          
            el: '#app',
            data: {
          
              // words: ''
              obj: {
          
                words: ''
              },
              result: '', // 翻译结果
              // timer: null // 延时器id
            },
            // 具体讲解：(1) watch语法 (2) 具体业务实现
            watch: {
          
              // 该方法会在数据变化时调用执行
              // newValue新值, oldValue老值（一般不用）
              // words (newValue) {
          
              //   console.log('变化了', newValue)
              // }
    
              'obj.words' (newValue) {
          
                // console.log('变化了', newValue)
                // 防抖: 延迟执行 → 干啥事先等一等，延迟一会，一段时间内没有再次触发，才执行
                clearTimeout(this.timer)
                this.timer = setTimeout(async () => {
          
                  const res = await axios({
          
                    url: 'https://applet-base-api-t.itheima.net/api/translate',
                    params: {
          
                      words: newValue
                    }
                  })
                  this.result = res.data.data
                  console.log(res.data.data)
                }, 300)
              }
            }
          })
        </script>
      </body>
    </html>

![在这里插入图片描述][835b061ddf81457fa0be1d6b7aa876c8.png]

### 3. 完整写法 ###

![在这里插入图片描述][00e7cd3f6b814771898e063dbd8c28e1.png]

<!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;
            font-size: 18px;
          }
          #app {
          
            padding: 10px 20px;
          }
          .query {
          
            margin: 10px 0;
          }
          .box {
          
            display: flex;
          }
          textarea {
          
            width: 300px;
            height: 160px;
            font-size: 18px;
            border: 1px solid #dedede;
            outline: none;
            resize: none;
            padding: 10px;
          }
          textarea:hover {
          
            border: 1px solid #1589f5;
          }
          .transbox {
          
            width: 300px;
            height: 160px;
            background-color: #f0f0f0;
            padding: 10px;
            border: none;
          }
          .tip-box {
          
            width: 300px;
            height: 25px;
            line-height: 25px;
            display: flex;
          }
          .tip-box span {
          
            flex: 1;
            text-align: center;
          }
          .query span {
          
            font-size: 18px;
          }
    
          .input-wrap {
          
            position: relative;
          }
          .input-wrap span {
          
            position: absolute;
            right: 15px;
            bottom: 15px;
            font-size: 12px;
          }
          .input-wrap i {
          
            font-size: 20px;
            font-style: normal;
          }
        </style>
      </head>
      <body>
        <div id="app">
          
          <div class="query">
            <span>翻译成的语言：</span>
            <select v-model="obj.lang">
              <option value="italy">意大利</option>
              <option value="english">英语</option>
              <option value="german">德语</option>
            </select>
          </div>
    
          
          <div class="box">
            <div class="input-wrap">
              <textarea v-model="obj.words"></textarea>
              <span><i>⌨️</i>文档翻译</span>
            </div>
            <div class="output-wrap">
              <div class="transbox">{
       { result }}</div>
            </div>
          </div>
        </div>
        <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
        <script src="https://cdn.jsdelivr.net/npm/axios/dist/axios.min.js"></script>
        <script>
          // 需求：输入内容，修改语言，都实时翻译
    
          // 接口地址：https://applet-base-api-t.itheima.net/api/translate
          // 请求方式：get
          // 请求参数：
          // （1）words：需要被翻译的文本（必传）
          // （2）lang： 需要被翻译成的语言（可选）默认值-意大利
          // -----------------------------------------------
       
          const app = new Vue({
          
            el: '#app',
            data: {
          
              obj: {
          
                words: '小黑',
                lang: 'italy'
              },
              result: '', // 翻译结果
            },
            watch: {
          
              obj: {
          
                deep: true, // 深度监视
                immediate: true, // 立刻执行，一进入页面handler就立刻执行一次
                handler (newValue) {
          
                  clearTimeout(this.timer)
                  this.timer = setTimeout(async () => {
          
                    const res = await axios({
          
                      url: 'https://applet-base-api-t.itheima.net/api/translate',
                      params: newValue
                    })
                    this.result = res.data.data
                    console.log(res.data.data)
                  }, 300)
                }
              }
    
    
              // 'obj.words' (newValue) {
          
              //   clearTimeout(this.timer)
              //   this.timer = setTimeout(async () => {
          
              //     const res = await axios({
          
              //       url: 'https://applet-base-api-t.itheima.net/api/translate',
              //       params: {
          
              //         words: newValue
              //       }
              //     })
              //     this.result = res.data.data
              //     console.log(res.data.data)
              //   }, 300)
              // }
            }
          })
        </script>
      </body>
    </html>

![在这里插入图片描述][f02c02dfe49b43b8bc4a633904648ed6.png]  
![在这里插入图片描述][795ebf7452eb4709a067c8cd03bfd004.png]

## 四、综合案例:水果购物车 ##

![在这里插入图片描述][8190bb909dce4b888a7ac7c0efffcbdb.png]

### 1. 渲染 ###

### 2. 删除和修改数量 ###

<!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" />
        <link rel="stylesheet" href="./css/inputnumber.css" />
        <link rel="stylesheet" href="./css/index.css" />
        <title>购物车</title>
      </head>
      <body>
        <div class="app-container" id="app">
          
          <div class="banner-box"><img src="http://autumnfish.cn/static/fruit.jpg" alt="" /></div>
          
          <div class="breadcrumb">
            <span>?</span>
            /
            <span>购物车</span>
          </div>
          
          <div class="main" v-if="fruitList.length > 0">
            <div class="table">
              
              <div class="thead">
                <div class="tr">
                  <div class="th">选中</div>
                  <div class="th th-pic">图片</div>
                  <div class="th">单价</div>
                  <div class="th num-th">个数</div>
                  <div class="th">小计</div>
                  <div class="th">操作</div>
                </div>
              </div>
              
              <div class="tbody">
                <div v-for="(item, index) in fruitList" :key="item.id" class="tr" :class="{ active: item.isChecked }">
                  <div class="td"><input type="checkbox" v-model="item.isChecked" /></div>
                  <div class="td"><img :src="item.icon" alt="" /></div>
                  <div class="td">{
       { item.price }}</div>
                  <div class="td">
                    <div class="my-input-number">
                      <button :disabled="item.num <= 1" class="decrease" @click="sub(item.id)"> - </button>
                      <span class="my-input__inner">{
       { item.num }}</span>
                      <button class="increase" @click="add(item.id)"> + </button>
                    </div>
                  </div>
                  <div class="td">{
       { item.num * item.price }}</div>
                  <div class="td"><button @click="del(item.id)">删除</button></div>
                </div>
              </div>
            </div>
            
            <div class="bottom">
              
              <label class="check-all">
                <input type="checkbox" />
                全选
              </label>
              <div class="right-box">
                
                <span class="price-box">总价  :  ¥ <span class="price">24</span></span>
                
                <button class="pay">结算( 6 )</button>
              </div>
            </div>
          </div>
          
          <div class="empty" v-else>?空空如也</div>
        </div>
        <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
        <script>
          const app = new Vue({
          
            el: '#app',
            data: {
          
              // 水果列表
              fruitList: [
                {
          
                  id: 1,
                  icon: 'http://autumnfish.cn/static/火龙果.png',
                  isChecked: true,
                  num: 2,
                  price: 6,
                },
                {
          
                  id: 2,
                  icon: 'http://autumnfish.cn/static/荔枝.png',
                  isChecked: false,
                  num: 7,
                  price: 20,
                },
                {
          
                  id: 3,
                  icon: 'http://autumnfish.cn/static/榴莲.png',
                  isChecked: false,
                  num: 3,
                  price: 40,
                },
                {
          
                  id: 4,
                  icon: 'http://autumnfish.cn/static/鸭梨.png',
                  isChecked: true,
                  num: 10,
                  price: 3,
                },
                {
          
                  id: 5,
                  icon: 'http://autumnfish.cn/static/樱桃.png',
                  isChecked: false,
                  num: 20,
                  price: 34,
                },
              ],
            },
            methods: {
          
              del (id) {
          
                this.fruitList = this.fruitList.filter(item => item.id !== id)
              },
              add (id) {
          
                // 1. 根据 id 找到数组中的对应项 → find
                const fruit = this.fruitList.find(item => item.id === id)
                // 2. 操作 num 数量
                fruit.num++
              },
              sub (id) {
          
                // 1. 根据 id 找到数组中的对应项 → find
                const fruit = this.fruitList.find(item => item.id === id)
                // 2. 操作 num 数量
                fruit.num--
              }
            }
          })
        </script>
      </body>
    </html>

### 3. 全选反选 ###

<!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" />
        <link rel="stylesheet" href="./css/inputnumber.css" />
        <link rel="stylesheet" href="./css/index.css" />
        <title>购物车</title>
      </head>
      <body>
        <div class="app-container" id="app">
          
          <div class="banner-box"><img src="http://autumnfish.cn/static/fruit.jpg" alt="" /></div>
          
          <div class="breadcrumb">
            <span>?</span>
            /
            <span>购物车</span>
          </div>
          
          <div class="main" v-if="fruitList.length > 0">
            <div class="table">
              
              <div class="thead">
                <div class="tr">
                  <div class="th">选中</div>
                  <div class="th th-pic">图片</div>
                  <div class="th">单价</div>
                  <div class="th num-th">个数</div>
                  <div class="th">小计</div>
                  <div class="th">操作</div>
                </div>
              </div>
              
              <div class="tbody">
                <div v-for="(item, index) in fruitList" :key="item.id" class="tr" :class="{ active: item.isChecked }">
                  <div class="td"><input type="checkbox" v-model="item.isChecked" /></div>
                  <div class="td"><img :src="item.icon" alt="" /></div>
                  <div class="td">{
       { item.price }}</div>
                  <div class="td">
                    <div class="my-input-number">
                      <button :disabled="item.num <= 1" class="decrease" @click="sub(item.id)"> - </button>
                      <span class="my-input__inner">{
       { item.num }}</span>
                      <button class="increase" @click="add(item.id)"> + </button>
                    </div>
                  </div>
                  <div class="td">{
       { item.num * item.price }}</div>
                  <div class="td"><button @click="del(item.id)">删除</button></div>
                </div>
              </div>
            </div>
            
            <div class="bottom">
              
              <label class="check-all">
                <input type="checkbox" v-model="isAll"/>
                全选
              </label>
              <div class="right-box">
                
                <span class="price-box">总价  :  ¥ <span class="price">24</span></span>
                
                <button class="pay">结算( 6 )</button>
              </div>
            </div>
          </div>
          
          <div class="empty" v-else>?空空如也</div>
        </div>
        <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
        <script>
          const app = new Vue({
          
            el: '#app',
            data: {
          
              // 水果列表
              fruitList: [
                {
          
                  id: 1,
                  icon: 'http://autumnfish.cn/static/火龙果.png',
                  isChecked: true,
                  num: 2,
                  price: 6,
                },
                {
          
                  id: 2,
                  icon: 'http://autumnfish.cn/static/荔枝.png',
                  isChecked: false,
                  num: 7,
                  price: 20,
                },
                {
          
                  id: 3,
                  icon: 'http://autumnfish.cn/static/榴莲.png',
                  isChecked: false,
                  num: 3,
                  price: 40,
                },
                {
          
                  id: 4,
                  icon: 'http://autumnfish.cn/static/鸭梨.png',
                  isChecked: true,
                  num: 10,
                  price: 3,
                },
                {
          
                  id: 5,
                  icon: 'http://autumnfish.cn/static/樱桃.png',
                  isChecked: false,
                  num: 20,
                  price: 34,
                },
              ],
            },
            computed: {
          
              // 默认计算属性：只能获取不能设置，要设置需要写完整写法
              // isAll () {
          
              //   // 必须所有的小选框都选中，全选按钮才选中 → every
              //   return this.fruitList.every(item => item.isChecked)
              // }
              
              // 完整写法 = get + set
              isAll: {
          
                get () {
          
                  return this.fruitList.every(item => item.isChecked)
                },
                set (value) {
          
                  // 基于拿到的布尔值，要让所有的小选框 同步状态
                  this.fruitList.forEach(item => item.isChecked = value)
                }
              }
            },
            methods: {
          
              del (id) {
          
                this.fruitList = this.fruitList.filter(item => item.id !== id)
              },
              add (id) {
          
                // 1. 根据 id 找到数组中的对应项 → find
                const fruit = this.fruitList.find(item => item.id === id)
                // 2. 操作 num 数量
                fruit.num++
              },
              sub (id) {
          
                // 1. 根据 id 找到数组中的对应项 → find
                const fruit = this.fruitList.find(item => item.id === id)
                // 2. 操作 num 数量
                fruit.num--
              }
            }
          })
        </script>
      </body>
    </html>

### 4. 统计总价 ###

<!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" />
        <link rel="stylesheet" href="./css/inputnumber.css" />
        <link rel="stylesheet" href="./css/index.css" />
        <title>购物车</title>
      </head>
      <body>
        <div class="app-container" id="app">
          
          <div class="banner-box"><img src="http://autumnfish.cn/static/fruit.jpg" alt="" /></div>
          
          <div class="breadcrumb">
            <span>?</span>
            /
            <span>购物车</span>
          </div>
          
          <div class="main" v-if="fruitList.length > 0">
            <div class="table">
              
              <div class="thead">
                <div class="tr">
                  <div class="th">选中</div>
                  <div class="th th-pic">图片</div>
                  <div class="th">单价</div>
                  <div class="th num-th">个数</div>
                  <div class="th">小计</div>
                  <div class="th">操作</div>
                </div>
              </div>
              
              <div class="tbody">
                <div v-for="(item, index) in fruitList" :key="item.id" class="tr" :class="{ active: item.isChecked }">
                  <div class="td"><input type="checkbox" v-model="item.isChecked" /></div>
                  <div class="td"><img :src="item.icon" alt="" /></div>
                  <div class="td">{
       { item.price }}</div>
                  <div class="td">
                    <div class="my-input-number">
                      <button :disabled="item.num <= 1" class="decrease" @click="sub(item.id)"> - </button>
                      <span class="my-input__inner">{
       { item.num }}</span>
                      <button class="increase" @click="add(item.id)"> + </button>
                    </div>
                  </div>
                  <div class="td">{
       { item.num * item.price }}</div>
                  <div class="td"><button @click="del(item.id)">删除</button></div>
                </div>
              </div>
            </div>
            
            <div class="bottom">
              
              <label class="check-all">
                <input type="checkbox" v-model="isAll"/>
                全选
              </label>
              <div class="right-box">
                
                <span class="price-box">总价  :  ¥ <span class="price">{
       { totalPrice }}</span></span>
                
                <button class="pay">结算( {
       { totalCount }} )</button>
              </div>
            </div>
          </div>
          
          <div class="empty" v-else>?空空如也</div>
        </div>
        <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
        <script>
          const app = new Vue({
          
            el: '#app',
            data: {
          
              // 水果列表
              fruitList: [
                {
          
                  id: 1,
                  icon: 'http://autumnfish.cn/static/火龙果.png',
                  isChecked: true,
                  num: 2,
                  price: 6,
                },
                {
          
                  id: 2,
                  icon: 'http://autumnfish.cn/static/荔枝.png',
                  isChecked: false,
                  num: 7,
                  price: 20,
                },
                {
          
                  id: 3,
                  icon: 'http://autumnfish.cn/static/榴莲.png',
                  isChecked: false,
                  num: 3,
                  price: 40,
                },
                {
          
                  id: 4,
                  icon: 'http://autumnfish.cn/static/鸭梨.png',
                  isChecked: true,
                  num: 10,
                  price: 3,
                },
                {
          
                  id: 5,
                  icon: 'http://autumnfish.cn/static/樱桃.png',
                  isChecked: false,
                  num: 20,
                  price: 34,
                },
              ],
            },
            computed: {
          
              // 默认计算属性：只能获取不能设置，要设置需要写完整写法
              // isAll () {
          
              //   // 必须所有的小选框都选中，全选按钮才选中 → every
              //   return this.fruitList.every(item => item.isChecked)
              // }
              
              // 完整写法 = get + set
              isAll: {
          
                get () {
          
                  return this.fruitList.every(item => item.isChecked)
                },
                set (value) {
          
                  // 基于拿到的布尔值，要让所有的小选框 同步状态
                  this.fruitList.forEach(item => item.isChecked = value)
                }
              },
              // 统计选中的总数 reduce
              totalCount () {
          
                return this.fruitList.reduce((sum, item) => {
          
                  if (item.isChecked) {
          
                    // 选中 → 需要累加
                    return sum + item.num
                  } else {
          
                    // 没选中 → 不需要累加
                    return sum
                  }
                }, 0)
              },
              // 总计选中的总价 num * price
              totalPrice () {
          
                return this.fruitList.reduce((sum, item) => {
          
                  if (item.isChecked) {
          
                    return sum + item.num * item.price
                  } else {
          
                    return sum
                  }
                }, 0)
              }
    
            },
            methods: {
          
              del (id) {
          
                this.fruitList = this.fruitList.filter(item => item.id !== id)
              },
              add (id) {
          
                // 1. 根据 id 找到数组中的对应项 → find
                const fruit = this.fruitList.find(item => item.id === id)
                // 2. 操作 num 数量
                fruit.num++
              },
              sub (id) {
          
                // 1. 根据 id 找到数组中的对应项 → find
                const fruit = this.fruitList.find(item => item.id === id)
                // 2. 操作 num 数量
                fruit.num--
              }
            }
          })
        </script>
      </body>
    </html>

### 5. 本地持久化 ###

<!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" />
        <link rel="stylesheet" href="./css/inputnumber.css" />
        <link rel="stylesheet" href="./css/index.css" />
        <title>购物车</title>
      </head>
      <body>
        <div class="app-container" id="app">
          
          <div class="banner-box"><img src="http://autumnfish.cn/static/fruit.jpg" alt="" /></div>
          
          <div class="breadcrumb">
            <span>?</span>
            /
            <span>购物车</span>
          </div>
          
          <div class="main" v-if="fruitList.length > 0">
            <div class="table">
              
              <div class="thead">
                <div class="tr">
                  <div class="th">选中</div>
                  <div class="th th-pic">图片</div>
                  <div class="th">单价</div>
                  <div class="th num-th">个数</div>
                  <div class="th">小计</div>
                  <div class="th">操作</div>
                </div>
              </div>
              
              <div class="tbody">
                <div v-for="(item, index) in fruitList" :key="item.id" class="tr" :class="{ active: item.isChecked }">
                  <div class="td"><input type="checkbox" v-model="item.isChecked" /></div>
                  <div class="td"><img :src="item.icon" alt="" /></div>
                  <div class="td">{
       { item.price }}</div>
                  <div class="td">
                    <div class="my-input-number">
                      <button :disabled="item.num <= 1" class="decrease" @click="sub(item.id)"> - </button>
                      <span class="my-input__inner">{
       { item.num }}</span>
                      <button class="increase" @click="add(item.id)"> + </button>
                    </div>
                  </div>
                  <div class="td">{
       { item.num * item.price }}</div>
                  <div class="td"><button @click="del(item.id)">删除</button></div>
                </div>
              </div>
            </div>
            
            <div class="bottom">
              
              <label class="check-all">
                <input type="checkbox" v-model="isAll"/>
                全选
              </label>
              <div class="right-box">
                
                <span class="price-box">总价  :  ¥ <span class="price">{
       { totalPrice }}</span></span>
                
                <button class="pay">结算( {
       { totalCount }} )</button>
              </div>
            </div>
          </div>
          
          <div class="empty" v-else>?空空如也</div>
        </div>
        <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
        <script>
          const defaultArr = [
                {
          
                  id: 1,
                  icon: 'http://autumnfish.cn/static/火龙果.png',
                  isChecked: true,
                  num: 2,
                  price: 6,
                },
                {
          
                  id: 2,
                  icon: 'http://autumnfish.cn/static/荔枝.png',
                  isChecked: false,
                  num: 7,
                  price: 20,
                },
                {
          
                  id: 3,
                  icon: 'http://autumnfish.cn/static/榴莲.png',
                  isChecked: false,
                  num: 3,
                  price: 40,
                },
                {
          
                  id: 4,
                  icon: 'http://autumnfish.cn/static/鸭梨.png',
                  isChecked: true,
                  num: 10,
                  price: 3,
                },
                {
          
                  id: 5,
                  icon: 'http://autumnfish.cn/static/樱桃.png',
                  isChecked: false,
                  num: 20,
                  price: 34,
                },
              ]
          const app = new Vue({
          
            el: '#app',
            data: {
          
              // 水果列表
              fruitList: JSON.parse(localStorage.getItem('list')) || defaultArr,
            },
            computed: {
          
              // 默认计算属性：只能获取不能设置，要设置需要写完整写法
              // isAll () {
          
              //   // 必须所有的小选框都选中，全选按钮才选中 → every
              //   return this.fruitList.every(item => item.isChecked)
              // }
              
              // 完整写法 = get + set
              isAll: {
          
                get () {
          
                  return this.fruitList.every(item => item.isChecked)
                },
                set (value) {
          
                  // 基于拿到的布尔值，要让所有的小选框 同步状态
                  this.fruitList.forEach(item => item.isChecked = value)
                }
              },
              // 统计选中的总数 reduce
              totalCount () {
          
                return this.fruitList.reduce((sum, item) => {
          
                  if (item.isChecked) {
          
                    // 选中 → 需要累加
                    return sum + item.num
                  } else {
          
                    // 没选中 → 不需要累加
                    return sum
                  }
                }, 0)
              },
              // 总计选中的总价 num * price
              totalPrice () {
          
                return this.fruitList.reduce((sum, item) => {
          
                  if (item.isChecked) {
          
                    return sum + item.num * item.price
                  } else {
          
                    return sum
                  }
                }, 0)
              }
            },
            methods: {
          
              del (id) {
          
                this.fruitList = this.fruitList.filter(item => item.id !== id)
              },
              add (id) {
          
                // 1. 根据 id 找到数组中的对应项 → find
                const fruit = this.fruitList.find(item => item.id === id)
                // 2. 操作 num 数量
                fruit.num++
              },
              sub (id) {
          
                // 1. 根据 id 找到数组中的对应项 → find
                const fruit = this.fruitList.find(item => item.id === id)
                // 2. 操作 num 数量
                fruit.num--
              }
            },
            watch: {
          
              fruitList: {
          
                deep: true,
                handler (newValue) {
          
                  // 需要将变化后的 newValue 存入本地 （转JSON）
                  localStorage.setItem('list', JSON.stringify(newValue))
                }
              }
            }
          })
        </script>
      </body>
    </html>

![在这里插入图片描述][ffa79b56096d4af8940383259d137c34.png]  
![在这里插入图片描述][2023e5bcd91c4de69aad190a9f4d667d.png]

## 总结 ##

欢迎各位留言交流以及批评指正，如果文章对您有帮助或者觉得作者写的还不错可以点一下关注,点赞，收藏支持一下。  
（博客的参考源码可以在我主页的资源里找到，如果在学习的过程中有什么疑问欢迎大家在评论区向我提出）

[Link 1]: https://www.captainbed.cn/dl
[88c791c2cc384a60b245e986af8fc4cb.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/123b9e35859a410e878a02c35aa5a0d3.png
[87b0a0fad53b4c9e875b7506b66d0e6f.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/ca8356ddb05c4a2c889ba8b1d02e89f3.png
[0f9b02d2d0a04b839c168ba1265e9de9.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/436d1a1e7d8040ec965fee8574ae5195.png
[9fd2755924cc485e979ab606d9b9167f.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/44e2abeb29bc46a18143be24da48ab51.png
[4fabee23246a42d191fc55f7478bef19.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/7bb22c5ac9604a10955d040151509645.png
[766a7da22ba74bb3b24591f181a6a394.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/8512009a4f5a4f98a8202fbb3968a35e.png
[7fe68639fbdd4e95b4385d2302c5abbd.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/bb58cfa25f7e47128d08da812f44a22b.png
[634f083b73484351aaf837c493d342e9.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/8eafd4b0f5f740218cf6ba8b3885cee2.png
[d0cfd0d897484e0ebe90fc82f0fed010.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/19f5ef1901f943bfbf5bff0d5c672f64.png
[8ed11efc7dcd4b6b90ffa37f919b8f0f.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/ef1c90a782724f7f88c5ada8e75d5309.png
[761b2e0d216c42728e758dece3f880ec.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/8a19ca9bf617490db66846d8ce89d32f.png
[107376518cba4ffead181a8c3c23a6b8.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/d9966afc458847cdab3b4a1447f7afbd.png
[d8d1908786b744e3998fb50d89ca291b.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/4b09505eb3fd466baf10f95966a8c44e.png
[a6d087a0514e43baa2151b52c215c0b9.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/9025edab9ced4b32a1462bdf217bebd2.png
[f6132ddc17c744d486dbe01e14cc445e.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/6071cae118004b6ba7c6941475258a19.png
[5378acda4f5b4eae841df7e3bd658983.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/61f0f20fad274992a45ddeff9ac292e4.png
[ca05f6e1c9404f19a9d1ee271d2c3e0d.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/e957c84e6c474007b5c66f73eb02ab3d.png
[3ced3875890a4bcca4a920c844288b5a.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/b7d4d030ded241c7ab14f446c9c4da8c.png
[242a9be1ebf64e72bbaa9cf7cd0256f5.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/b24426ff92a349c78011281bc7635ddf.png
[0c5f2187f70b4473bd815207e853ec8c.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/25399288f09b4f8bb38c66139e073ee5.png
[307e33ed6b5343faab5431205a13fcb1.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/539ae49b9b8e4a41a08125ae10872fcb.png
[ae90dcb74d074b07b77af272b975c569.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/50a8fe607f3f4138b27e96aee9272d8c.png
[835b061ddf81457fa0be1d6b7aa876c8.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/64bba5f1a6ca4a4d945378c8b17eebcb.png
[00e7cd3f6b814771898e063dbd8c28e1.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/48c9ffd4125d4c4fa1141c8e84125ab9.png
[f02c02dfe49b43b8bc4a633904648ed6.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/a57b0e490b784643a50d88154e3f5bd8.png
[795ebf7452eb4709a067c8cd03bfd004.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/701c2ee9d7c24aa99fea9d04b33ec45f.png
[8190bb909dce4b888a7ac7c0efffcbdb.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/60e4f860332e45389102d6bbf200824f.png
[ffa79b56096d4af8940383259d137c34.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/90b3bc28cd784adba16c2460fff9f1fb.png
[2023e5bcd91c4de69aad190a9f4d667d.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/20/8bbc1eba93b44d00983ec6c8a08efa0d.png