这个示例是模仿官网示例样式和功能用我自己的方式写的，基本上没有看官网的源码，只参考自定义指令。让我们一步步来探讨一下。官网demo

要实现的功能

1. 单条添加todo
2. 单条删除todo
3. 双击编辑todo
4. 单条todo已完成相应样式状态改变
5. 全部todo是已完成相应样式状态改变
6. 清除全部已完成todos
7. 待办todos数量显示
8. 所有todos，已完成todos，未完成todos筛选

单条添加todo

<input type="text" class="todos_add" placeholder="What needs to be done?" 
@keyup.enter="addTodo($event.target)" //绑定enter事件
ref="currentInput">//操作input元素使enter一下之后清空输入框内容

data() {//一些初始化数据
 return {
 todolists: [],
 dataStatus: ["All", "Active", "Completed"],
 dataStatusIndex: 0,
 whichShow: true,
 defaultShow: true
 }
},
addTodo(e) { //添加todo
 var val = e.value
 if (val === "") {return} //如果输入内容为空则立即返回
 this.todoLists = this.todoLists.concat({//使用concat这个api添加todo
 value: val, //输入内容
 isEditing: false, //是否在编辑状态
 isActive: false, //删除X图标是否激活
 isChecked: false //是否已完成
 })
 this.$refs.currentInput.value = "" //按下enter添加todo之后把输入框value清零
 window.localStorage.setItem("content",JSON.stringify(this.todoLists))//使用localStorage以JSON格式存储数据
},

把每条todo的对应状态都存在同一个对象当中，在操作改变todo状态的时候不会被统一处理，使得每条todo都有单独的状态。

单条删除todo

 <li class="content_todoList"
 v-for="(list,index) in todoLists" 
 @mouseover="list.isActive = true" //鼠标移入todo改变对应todo的isActive状态
 @mouseleave="list.isActive=false" //鼠标移出todo改变对应todo的isActive状态
 <span class="el-icon-close content_todoList_delete" 
 :class="{show: list.isActive}" //动态绑定class使鼠标移动到某一todo显示X图标
 @click="deleteTodo(index)"> //绑定删除单条todo事件
 </span>
</li>

deleteTodo(index) { //删除单条todo
 this.todoLists.splice(index, 1)//使用splice的api
 window.localStorage.setItem("content",JSON.stringify(todoLists)) //以JSON格式存储数据//localStorage存储数据
},

在每个li元素上绑定了鼠标移入和移除的事件来动态的改变每个todo的isActive，然后再使用isActive动态显示class。

双击编辑todo&&单条todo已完成

<input type="checkbox" class="checkBox" 
v-model="list.isChecked">//双向绑定isChecked

<div class="content_todoList_main" 
@dblclick="toEdit(list)" //双击事件
v-show="!list.isEditing" //切换元素
:class="{deleted:list.isChecked}"> //动态绑定class该表已完成todo样式
{{list.value}}
</div>

<input type="text" class="content_todoList_main main_input" 
v-model="list.value" //双向绑定可输入value
v-show="list.isEditing" //切换元素
v-todo-focus="list.value" //自定义指令，双击之后自动focus对焦
@blur="unEdit(list)"> //绑定blur失去焦点事件

methods: {
 toEdit(obj) { //使添加的todothing可编辑
 obj.isEditing = true
 },
 
 unEdit(obj) { //使添加的todothing不可编辑
 obj.isEditing = false
 },
}

directives: { //自定义focus指令,需要一个binding参数做判断
 "todo-focus": function (el, binding) {
 if (binding.value) {
 el.focus()
 }
 }
}

通过每个todo里的isEditing属性控制show和是否可编辑两个状态，双击div之后改变当前todo的isEditing为true，从而显示为input，input失去焦点之后再通过blur事件改为false。

通过todo的idChecked来控制是否已完成，从而动态改变样式。

全部todos已完成

<span 
class="icon-down el-icon-arrow-down" //使用element库做向下箭头icon
v-show="todoLists.length>0" //通过todoLists控制是否显示向下箭头icon
@click="selectAllTodos"></span> //全部已完成事件

selectAllTodos() { //设置所有todo为已完成,使用map的api通过todo的isChecked属性操作
 this.todoLists.map(todo => todo.isChecked = todo.isChecked ? false : true)
}

待办todos数量显示

<div class="data_times" v-show="times === 0"> //times为0显示item，大于0显示items，细节注定成败
 <span>{{times}}</span>  item left
</div>
<div class="data_times" v-show="times > 0">
<span>{{times}}</span>  items left</div>

computed: {
 times() { //使用计算属性计算待办todos的次数 
 let todoArr = this.todoLists
 let times = 0
 for (let i = 0; i < todoArr.length; i++) {
 if (todoArr[i].isChecked === false) {
 times++
 }
 }
 return times
 }
},

使用了计算属性对todoLists计算，用for循环刷选出idChecked为true的累加，最后返回times。

清除全部已完成todos

<div class="data_clearTodos" 
@click="clearTodos" 
v-show="times < todoLists.length"> //如果待办事件次数小于总todoLists长度就显示“clear completed”
 <a href="#" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >clear completed</a>
</div>

<div class="data_clearTodos" 
@click="clearTodos" 
v-show="times === todoLists.length"> //如果待办事件次数等于总todoLists长度就显示“clear completed”
 <a href="#" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" ></a>
</div>

clearTodos() { //清空已完成的todoLists，使用filter的api进行筛选
 this.todoLists = this.todoLists.filter(todo => todo.isChecked === false)
 window.localStorage.setItem("content",JSON.stringify(this.todoLists)) //以json格式存储数据
},

如果待办todos的times小于todoLists长度，就证明有已完成的todo，就可以显示“clear completed”，如果相等就说明没有已完成的todo。

三种状态筛选

所有todos，已完成todos，未完成todos筛选

<li class="content_todoList" 
v-show="defaultShow || (whichShow?list.isChecked:!list.isChecked)">

<div class="data_status">
 <a href="#" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" 
 :class="{active: index === dataStatusIndex}" //动态class实现tab切换
 v-for="(item ,index) in dataStatus" v-for循环
 @click="switchStatus(index)" //切换不同tab显示内容
 :key="index">
 {{item}}
 </a>
</div>

switchStatus(index) { //通过if条件判断操作
 this.dataStatusIndex = index
 if (this.dataStatus[index] === "Active") {
 this.defaultShow = false
 this.whichShow = false
 } else if (this.dataStatus[index] === "Completed") {
 this.defaultShow = false
 this.whichShow = true
 } else if (this.dataStatus[index] === "All") {
 this.defaultShow = true
 }
},

我这里是同时if条件句判断操作，有点麻烦，目前还没有想出来其他方案。在li元素使用三元运算符和或运算符进行操作显示不同状态的todos。

完整代码

<style>
 * {
 padding: 0;
 margin: 0;
 box-sizing: border-box;
 }

 input {
 outline: none;
 }

 ul,
 li,
 ol {
 list-style: none;
 }

 #app {
 width: 800px;
 height: 900px;
 margin: 0 auto;
 text-align: center;
 background-color: rgb(245, 245, 245);
 padding: 24px 0;
 }

 #app .header {
 font-size: 48px;
 }

 .content {
 width: 72%;
 margin: 0 auto;
 box-shadow: 0 3px 3px 2px rgba(0, 0, 0, 0.25);
 position: relative;
 }

 .icon-down {
 position: absolute;
 font-size: 24px;
 top: 16px;
 left: 16px;
 cursor: pointer;
 }

 #app .content .todos_add {
 width: 100%;
 height: 56px;
 padding: 16px 56px;
 font-size: 24px;
 border: 1px solid transparent;
 }

 .content_todoLists {
 position: relative;
 z-index: 3;
 }

 .content_todoList {
 display: flex;
 flex-direction: row;
 border-top: 1px solid #ccc;
 font-size: 24px;
 padding: 8px;
 background-color: white;
 align-items: center;
 }

 .checkBox {
 width: 20px;
 height: 20px;
 margin-left: 10px;
 }

 .content_todoList_main {
 flex: 1;
 text-align: left;
 margin-left: 16px;
 font-size: 20px;
 padding: 6px 0;
 }

 .main_input {
 position: relative;
 z-index: 1;
 }

 .content_todoList_delete {
 position: absolute;
 right: 16px;
 color: rgb(252, 55, 55);
 font-weight: 500;
 display: none;
 cursor: pointer;
 }

 .show {
 display: block;
 }

 .deleted {
 text-decoration-line: line-through;
 color: #bbb;
 }

 .show:hover {
 color: rgb(255, 0, 0);
 font-weight: 700;
 }

 ::-moz-placeholder {
 color: rgb(221, 218, 218);
 }

 ::-webkit-input-placeholder {
 color: rgb(221, 218, 218);
 }

 :-ms-input-placeholder {
 color: rgb(221, 218, 218);
 }

 .data {
 display: flex;
 justify-content: space-between;
 padding: 8px;
 font-size: 14px;
 font-weight: 300;
 color: rgb(145, 145, 145);
 }

 a {
 text-decoration: none;
 color: rgb(145, 145, 145);
 }

 .data_times {
 width: 73px;
 }

 .data_clearTodos {
 width: 142px;
 }

 .data_status a {
 display: inline-block;
 border: 1px solid transparent;
 border-radius: 2px;
 padding: 1px 4px;
 margin: 0 2px;
 }

 .data_status a:hover {
 border-color: #bbb;
 }

 .data_clearTodos a:hover {
 text-decoration-line: underline;
 }

 .active {
 box-shadow: 0 0 1px black;
 }
</style>

<body>
 <div id="app">
 <header class="header">todos</header>
 <div class="content">
 <span class="icon-down el-icon-arrow-down" 
 v-show="todoLists.length>0" 
 @click="selectAllTodos">
 </span>
 <input type="text" class="todos_add" placeholder="What needs to be done?" 
 @keyup.enter="addTodo($event.target)" 
 ref="currentInput">
 <ul class="content_todoLists">
 <li v-for="(list,index) in todoLists" class="content_todoList" 
 @mouseover="list.isActive = true" 
 @mouseleave="list.isActive=false"
 v-show="defaultShow || (whichShow?list.isChecked:!list.isChecked)">
 <input type="checkbox" class="checkBox" v-model="list.isChecked">
 <div class="content_todoList_main" @dblclick="toEdit(list)" v-show="!list.isEditing" :class="{deleted:list.isChecked}">
 {{list.value}}
 </div>
 <input type="text" class="content_todoList_main main_input" 
 v-model="list.value" 
 v-show="list.isEditing" 
 v-todo-focus="list.value"
 @blur="unEdit(list)">
 <span class="el-icon-close content_todoList_delete" :class="{show: list.isActive}" @click="deleteTodo(index)"></span>
 </li>
 </ul>
 <div class="data" v-show="todoLists.length>0">
 <div class="data_times" v-show="times === 0">
 <span>{{times}}</span> item left
 </div>
 <div class="data_times" v-show="times > 0">
 <span>{{times}}</span> items left
 </div>
 <div class="data_status">
 <a href="#" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" :class="{active:index === dataStatusIndex}" v-for="(item,index) in dataStatus" @click="switchStatus(index)" :key="index">
 {{item}}
 </a>
 </div>
 <div class="data_clearTodos" @click="clearTodos" v-show="times < todoLists.length">
 <a href="#" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >clear completed</a>
 </div>
 <div class="data_clearTodos" @click="clearTodos" v-show="times === todoLists.length">
 <a href="#" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" ></a>
 </div>
 </div>
 </div>
 </div>
</body>
<script>
 let vm = new Vue({
 el: "#app",
 data() {
 return {
 todoLists: [],
 dataStatus: ["All", "Active", "Completed"],
 dataStatusIndex: 0,
 whichShow: true,
 defaultShow: true
 }
 },
 computed: {
 times() { //使用计算属性计算待办todos的次数 
 let todoArr = this.todoLists
 let times = 0
 for (let i = 0; i < todoArr.length; i++) {
 if (todoArr[i].isChecked === false) {
 times++
 }
 }
 return times
 }
 },
 methods: {
 toEdit(obj) { //使添加的todo可编辑
 obj.isEditing = true
 },
 unEdit(obj) { //使添加的todo不可编辑
 obj.isEditing = false
 },
 addTodo(e) { //添加todo
 var val = e.value
 if (val === "") {
 return
 } //如果输入内容为空则立即返回
 this.todoLists = this.todoLists.concat({ //使用concat这个api添加todo
 value: val, //输入内容
 isEditing: false, //是否在编辑状态
 isActive: false, //删除X图标是否激活
 isChecked: false //是否已完成
 })
 this.$refs.currentInput.value = "" //按下enter添加todo之后把输入框value清零
 window.localStorage.setItem("content", JSON.stringify(this.todoLists)) //使用localStorage以JSON格式存储数据
 },
 deleteTodo(index) { //删除todo
 this.todoLists.splice(index, 1)
 window.localStorage.setItem("content", JSON.stringify(this.todoLists)) //以json格式存储数据
 },
 switchStatus(index) { //试下下方三个状态切换，略麻烦
 this.dataStatusIndex = index
 if (this.dataStatus[index] === "Active") {
 this.defaultShow = false
 this.whichShow = false
 } else if (this.dataStatus[index] === "Completed") {
 this.defaultShow = false
 this.whichShow = true
 } else if (this.dataStatus[index] === "All") {
 this.defaultShow = true
 }
 },
 clearTodos() { //清空已完成的todoLists
 this.todoLists = this.todoLists.filter(todo => todo.isChecked === false)
 window.localStorage.setItem("content", JSON.stringify(this.todoLists)) //以json格式存储数据
 },
 selectAllTodos() { //设置所有todo为已完成
 this.todoLists.map(todo => todo.isChecked = todo.isChecked ? false : true)
 }
 },
 directives: { //自定义focus指令
 "todo-focus": function (el, binding) {
 if (binding.value) {
 el.focus()
 }
 }
 },
 created() {
 let myStorage = window.localStorage.getItem('content')
 this.todoLists = JSON.parse(myStorage) || [] //因为todoLists初始值是null,使用或运算符，如果为null设为空数组
 }
 })
</script>