1、模块化开发
2、主要逻辑都在App.vue中实现
3、子组件传给父组件用this.$emit
4、父组件传子组件，子组件用props接收

App.vue

<template>
  <section id="app">
    <ToDoHeader 
    @add="handleAdd"></ToDoHeader>
    <ToDoMain
    :list="list"
    @delId="del"
    ></ToDoMain>
    <ToDoFooter
    v-show="list.length != 0"
    :list="list"
    @clear="clear"
    ></ToDoFooter>
</section>
</template>

<script>
import ToDoHeader from './components/ToDoHeader.vue';
import ToDoMain from './components/ToDoMain.vue';
import ToDoFooter from './components/ToDoFooter.vue';
export default {
  components: {
    ToDoHeader, ToDoMain, ToDoFooter
  },

  data () {
    return {
      // 持久化存储，保存在本地
      list: JSON.parse(localStorage.getItem('list')) ||
      [
        {id: 1, name: '打篮球'},
        {id: 2, name: '打球'},
        {id: 3, name: '球'},
      ],
    }
  },
  methods: {
    // ToDoHeader的添加任务
    handleAdd(todoName) {
      this.list.push({
        id: +new Date(), name: todoName
      });
      console.log('list.length ->', this.list.length);
    },
    // ToDoMain的删除按钮
    del (id) {
      console.log('delId ->', id);
      this.list = this.list.filter(item => item.id != id);
    },
    // ToDoFooter的清空任务
    clear () {
      this.list = []
    },
  },

  // 持久化存储
  watch: {
    list: {
      deep: true,
      handler (newValue) {
        localStorage.setItem('list', JSON.stringify(newValue));
      }
    }
  }
}
</script>

<style>

</style>

ToDoHeader.vue

<template>
    <!-- 输入框 -->
    <header class="header">
        <h1>小黑记事本</h1>
        <input 
        placeholder="请输入任务" 
        class="new-todo" 
        @keyup.enter="handleAdd" 
        v-model="todoName" />
        <button @click="handleAdd" class="add">添加任务</button>
    </header>
</template>

<script>
export default {

    data () {
        return {
        todoName: "",
        }
    },
    methods: {
        handleAdd() {
           this.$emit('add', this.todoName);
        }
    }
}
</script>

<style>

</style>

ToDoMain.vue

<template>
  <!-- 列表区域 -->
  <section class="main">
      <ul class="todo-list">
        <li class="todo" v-for="(item, idx) in list" :key="item.id">
          <div class="view">
            <span class="index">{{ idx+1 }}</span> <label>{{ item.name }}</label>
            <button @click="del(item.id)" class="destroy"></button>
          </div>
        </li>
      </ul>
    </section>
</template>

<script>
export default {
  props: {
    list: Array,
  },
  methods: {
    del (id) {
      this.$emit('delId', id)
    }
  }
}
</script>

<style scoped>  
  button {
    cursor: pointer;
  }
</style>

ToDoFooter.vue

<template>
  <!-- 统计和清空 -->
  <footer class="footer">
      <!-- 统计 -->
      <span class="todo-count">合 计:<strong>{{ list.length }} </strong></span>
      <!-- 清空 -->
      <button class="clear-completed" @click="clear">
        清空任务
      </button>
    </footer>
</template>

<script>
export default {
  props:{
    list: Array
  },
  methods: {
    clear () {
      this.$emit('clear');
    }
  }
}
</script>

<style>

</style>

style.css

html,
body {
    margin: 0;
    padding: 0;
}

body {
    background: #fff;
}

button {
    margin: 0;
    padding: 0;
    border: 0;
    background: none;
    font-size: 100%;
    vertical-align: baseline;
    font-family: inherit;
    font-weight: inherit;
    color: inherit;
    -webkit-appearance: none;
    appearance: none;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

body {
    font: 14px 'Helvetica Neue', Helvetica, Arial, sans-serif;
    line-height: 1.4em;
    background: #f5f5f5;
    color: #4d4d4d;
    min-width: 230px;
    max-width: 550px;
    margin: 0 auto;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    font-weight: 300;
}

:focus {
    outline: 0;
}

.hidden {
    display: none;
}

#app {
    background: #fff;
    margin: 180px 0 40px 0;
    padding: 15px;
    position: relative;
    box-shadow: 0 2px 4px 0 rgba(0, 0, 0, 0.2), 0 25px 50px 0 rgba(0, 0, 0, 0.1);
}

#app .header input {
    border: 2px solid rgba(175, 47, 47, 0.8);
    border-radius: 10px;
}

#app .add {
    position: absolute;
    right: 15px;
    top: 15px;
    height: 68px;
    width: 140px;
    text-align: center;
    background-color: rgba(175, 47, 47, 0.8);
    color: #fff;
    cursor: pointer;
    font-size: 18px;
    border-radius: 0 10px 10px 0;
}

#app input::-webkit-input-placeholder {
    font-style: italic;
    font-weight: 300;
    color: #e6e6e6;
}

#app input::-moz-placeholder {
    font-style: italic;
    font-weight: 300;
    color: #e6e6e6;
}

#app input::input-placeholder {
    font-style: italic;
    font-weight: 300;
    color: gray;
}

#app h1 {
    position: absolute;
    top: -120px;
    width: 100%;
    left: 50%;
    transform: translateX(-50%);
    font-size: 60px;
    font-weight: 100;
    text-align: center;
    color: rgba(175, 47, 47, 0.8);
    -webkit-text-rendering: optimizeLegibility;
    -moz-text-rendering: optimizeLegibility;
    text-rendering: optimizeLegibility;
}

.new-todo,
.edit {
    position: relative;
    margin: 0;
    width: 100%;
    font-size: 24px;
    font-family: inherit;
    font-weight: inherit;
    line-height: 1.4em;
    border: 0;
    color: inherit;
    padding: 6px;
    box-shadow: inset 0 -1px 5px 0 rgba(0, 0, 0, 0.2);
    box-sizing: border-box;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

.new-todo {
    padding: 16px;
    border: none;
    background: rgba(0, 0, 0, 0.003);
    box-shadow: inset 0 -2px 1px rgba(0, 0, 0, 0.03);
}

.main {
    position: relative;
    z-index: 2;
}

.todo-list {
    margin: 0;
    padding: 0;
    list-style: none;
    overflow: hidden;
}

.todo-list li {
    position: relative;
    font-size: 24px;
    height: 60px;
    box-sizing: border-box;
    border-bottom: 1px solid #e6e6e6;
}

.todo-list li:last-child {
    border-bottom: none;
}

.todo-list .view .index {
    position: absolute;
    color: gray;
    left: 10px;
    top: 20px;
    font-size: 22px;
}

.todo-list li .toggle {
    text-align: center;
    width: 40px;
    /* auto, since non-WebKit browsers doesn't support input styling */
    height: auto;
    position: absolute;
    top: 0;
    bottom: 0;
    margin: auto 0;
    border: none;
    /* Mobile Safari */
    -webkit-appearance: none;
    appearance: none;
}

.todo-list li .toggle {
    opacity: 0;
}

.todo-list li .toggle+label {
    /*
        Firefox requires `#` to be escaped - https://bugzilla.mozilla.org/show_bug.cgi?id=922433
        IE and Edge requires *everything* to be escaped to render, so we do that instead of just the `#` - https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/7157459/
    */
    background-image: url('data:image/svg+xml;utf8,%3Csvg%20xmlns%3D%22http%3A//www.w3.org/2000/svg%22%20width%3D%2240%22%20height%3D%2240%22%20viewBox%3D%22-10%20-18%20100%20135%22%3E%3Ccircle%20cx%3D%2250%22%20cy%3D%2250%22%20r%3D%2250%22%20fill%3D%22none%22%20stroke%3D%22%23ededed%22%20stroke-width%3D%223%22/%3E%3C/svg%3E');
    background-repeat: no-repeat;
    background-position: center left;
}

.todo-list li .toggle:checked+label {
    background-image: url('data:image/svg+xml;utf8,%3Csvg%20xmlns%3D%22http%3A//www.w3.org/2000/svg%22%20width%3D%2240%22%20height%3D%2240%22%20viewBox%3D%22-10%20-18%20100%20135%22%3E%3Ccircle%20cx%3D%2250%22%20cy%3D%2250%22%20r%3D%2250%22%20fill%3D%22none%22%20stroke%3D%22%23bddad5%22%20stroke-width%3D%223%22/%3E%3Cpath%20fill%3D%22%235dc2af%22%20d%3D%22M72%2025L42%2071%2027%2056l-4%204%2020%2020%2034-52z%22/%3E%3C/svg%3E');
}

.todo-list li label {
    word-break: break-all;
    padding: 15px 15px 15px 60px;
    display: block;
    line-height: 1.2;
    transition: color 0.4s;
}

.todo-list li.completed label {
    color: #d9d9d9;
    text-decoration: line-through;
}

.todo-list li .destroy {
    display: none;
    position: absolute;
    top: 0;
    right: 10px;
    bottom: 0;
    width: 40px;
    height: 40px;
    margin: auto 0;
    font-size: 30px;
    color: #cc9a9a;
    margin-bottom: 11px;
    transition: color 0.2s ease-out;
}

.todo-list li .destroy:hover {
    color: #af5b5e;
}

.todo-list li .destroy:after {
    content: '×';
}

.todo-list li:hover .destroy {
    display: block;
}

.todo-list li .edit {
    display: none;
}

.todo-list li.editing:last-child {
    margin-bottom: -1px;
}

.footer {
    color: #777;
    padding: 10px 15px;
    height: 20px;
    text-align: center;
    border-top: 1px solid #e6e6e6;
}

.footer:before {
    content: '';
    position: absolute;
    right: 0;
    bottom: 0;
    left: 0;
    height: 50px;
    overflow: hidden;
    box-shadow: 0 1px 1px rgba(0, 0, 0, 0.2), 0 8px 0 -3px #f6f6f6,
        0 9px 1px -3px rgba(0, 0, 0, 0.2), 0 16px 0 -6px #f6f6f6,
        0 17px 2px -6px rgba(0, 0, 0, 0.2);
}

.todo-count {
    float: left;
    text-align: left;
}

.todo-count strong {
    font-weight: 300;
}

.filters {
    margin: 0;
    padding: 0;
    list-style: none;
    position: absolute;
    right: 0;
    left: 0;
}

.filters li {
    display: inline;
}

.filters li a {
    color: inherit;
    margin: 3px;
    padding: 3px 7px;
    text-decoration: none;
    border: 1px solid transparent;
    border-radius: 3px;
}

.filters li a:hover {
    border-color: rgba(175, 47, 47, 0.1);
}

.filters li a.selected {
    border-color: rgba(175, 47, 47, 0.2);
}

.clear-completed,
html .clear-completed:active {
    float: right;
    position: relative;
    line-height: 20px;
    text-decoration: none;
    cursor: pointer;
}

.clear-completed:hover {
    text-decoration: underline;
}

.info {
    margin: 50px auto 0;
    color: #bfbfbf;
    font-size: 15px;
    text-shadow: 0 1px 0 rgba(255, 255, 255, 0.5);
    text-align: center;
}

.info p {
    line-height: 1;
}

.info a {
    color: inherit;
    text-decoration: none;
    font-weight: 400;
}

.info a:hover {
    text-decoration: underline;
}

/*
    Hack to remove background from Mobile Safari.
    Can't use it globally since it destroys checkboxes in Firefox
*/
@media screen and (-webkit-min-device-pixel-ratio: 0) {

    .toggle-all,
    .todo-list li .toggle {
        background: none;
    }

    .todo-list li .toggle {
        height: 40px;
    }
}

@media (max-width: 430px) {
    .footer {
        height: 50px;
    }

    .filters {
        bottom: 10px;
    }
}

main.js

import Vue from 'vue'
import App from './App.vue'
import './style/index.css'
Vue.config.productionTip = false

new Vue({
  render: h => h(App),
}).$mount('#app')