通过10个实例小练习，快速入门熟练 Vue3.0 核心新特性

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    Vue3.0 发 beta 版都有一段时间了，正式版也不远了，所以真的要学习一下 Vue3.0 的语法了。

    GitHub 博客地址: https://github.com/biaochenxu...

    环境搭建

    $ git pull https://github.com/vuejs/vue-next.git
$ cd vue-next && yarn

    下载完成之后打开代码， 开启 sourceMap :

    • tsconfig.json 把 sourceMap 字段修改为 true: "sourceMap": true
    • rollup.config.js 在 rollup.config.js 中，手动键入： output.sourcemap = true
    • 生成 vue 全局的文件：yarn dev
    • 在根目录创建一个 demo 目录用于存放示例代码，并在 demo 目录下创建 html 文件，引入构建后的 vue 文件

    api 的使用都是很简单的，下文的内容，看例子代码就能懂了的，所以下面的例子不会做过多解释。

    reactive

    reactive: 创建响应式数据对象

    setup 函数是个新的入口函数，相当于 vue2.x 中 beforeCreate 和 created，在 beforeCreate 之后 created 之前执行。

    <head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Hello Vue3.0</title>
    <style>
        body,
        #app {
            text-align: center;
            padding: 30px;
        }
    </style>
    <script src="../../packages/vue/dist/vue.global.js"></script>
</head>
<body>
    <h3>reactive</h3>
    <div id='app'></div>
</body>
<script>
    const { createApp, reactive } = Vue
    const App = {
        template: `
            <button @click='click'>reverse</button> 
            <div style="margin-top: 20px">{{ state.message }}</div>
        `,
        setup() {
            console.log('setup ');

            const state = reactive({
                message: 'Hello Vue3!!'
            })

            click = () => {
                state.message = state.message.split('').reverse().join('')
            }

            return {
                state,
                click
            }
        }
    }
    createApp(App).mount('#app')
</script>
</html>

    ref & isRef

    ref : 创建一个响应式的数据对象
    isRef : 检查值是否是 ref 的引用对象。
    <html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Hello Vue3.0</title>
    <style>
        body,
        #app {
            text-align: center;
            padding: 30px;
        }
    </style>
    <script src="../../packages/vue/dist/vue.global.js"></script>
</head>
<body>
    <h3>ref & isRef</h3>
    <div id='app'></div>
</body>
<script>
    const { createApp, reactive, ref, isRef } = Vue
    const App = {
        template: `
            <button @click='click'>count++</button> 
            <div style="margin-top: 20px">{{ count }}</div>
        `,
        setup() {
            const count = ref(0);
            console.log("count.value：", count.value)  // 0

            count.value++
            console.log("count.value：", count.value)  // 1

            // 判断某值是否是响应式类型
            console.log('count is ref:', isRef(count))

            click = () => {
                count.value++;
                console.log("click count.value：", count.value) 
            }

            return {
                count,
                click,
            }
        }
    }
    createApp(App).mount('#app')
</script>
</html>

    Template Refs

    使用 Composition API 时，反应性引用和模板引用的概念是统一的。

    为了获得对模板中元素或组件实例的引用，我们可以像往常一样声明 ref 并从 setup() 返回。

    <html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Hello Vue3.0</title>
    <style>
        body,
        #app {
            text-align: center;
            padding: 30px;
        }
    </style>
    <script src="../../packages/vue/dist/vue.global.js"></script>
</head>
<body>
    <h3>Template Refs</h3>
    <div id='app'></div>
</body>
<script>
    const { createApp, reactive, ref, isRef, toRefs, onMounted, onBeforeUpdate } = Vue
    const App = {
        template: `
            <button @click='click'>count++</button> 
            <div ref="count" style="margin-top: 20px">{{ count }}</div>
        `,
        setup() {
            const count = ref(null);

            onMounted(() => {
                // the DOM element will be assigned to the ref after initial render
                console.log(count.value) // <div/>
            })

            click = () => {
                count.value++;
                console.log("click count.value：", count.value) 
            }

            return {
                count,
                click
            }
        }
    }
    
    createApp(App).mount('#app')
</script>
</html>

    <html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Hello Vue3.0</title>
    <style>
        body,
        #app {
            text-align: center;
            padding: 30px;
        }
    </style>
    <script src="../../packages/vue/dist/vue.global.js"></script>
</head>
<body>
    <h3>Template Refs</h3>
    <div id='app'></div>
</body>
<script>
    const { createApp, reactive, ref, isRef, toRefs, onMounted, onBeforeUpdate } = Vue
    const App = {
        template: `
            <div v-for="(item, i) in list" :ref="el => { divs[i] = el }">
                {{ item }}
            </div>
        `,
        setup() {
            const list = reactive([1, 2, 3])
            const divs = ref([])

            // make sure to reset the refs before each update
            onBeforeUpdate(() => {
                divs.value = []
            })

            onMounted(() => {
                // the DOM element will be assigned to the ref after initial render
                console.log(divs.value) // [<div/>]
            })

            return {
                list,
                divs
            }
        }
    }
    
    createApp(App).mount('#app')
</script>
</html>

    toRefs

    toRefs : 将响应式数据对象转换为单一响应式对象

    将一个 reactive 代理对象打平，转换为 ref 代理对象，使得对象的属性可以直接在 template 上使用。

    <html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Hello Vue3.0</title>
    <style>
        body,
        #app {
            text-align: center;
            padding: 30px;
        }
    </style>
    <script src="../../packages/vue/dist/vue.global.js"></script>
</head>
<body>
    <h3>toRefs</h3>
    <div id='app'></div>
</body>
<script>
    const { createApp, reactive, ref, isRef, toRefs } = Vue
    const App = {
        // template: `
        //     <button @click='click'>reverse</button> 
        //     <div style="margin-top: 20px">{{ state.message }}</div>
        // `,
        // setup() {
        //     const state = reactive({
        //         message: 'Hello Vue3.0!!'
        //     })

        //     click = () => {
        //         state.message = state.message.split('').reverse().join('')
        //         console.log('state.message: ', state.message)
        //     }

        //     return {
        //         state,
        //         click
        //     }
        // }

        template: `
            <button @click='click'>count++</button> 
            <div style="margin-top: 20px">{{ message }}</div>
        `,
        setup() {
            const state = reactive({
                message: 'Hello Vue3.0!!'
            })

            click = () => {
                state.message = state.message.split('').reverse().join('')
                console.log('state.message: ', state.message)
            }

            return {
                click,
                ...toRefs(state)
            }
        }
    }
    createApp(App).mount('#app')
</script>
</html>

    computed

    computed : 创建计算属性
    <html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Hello Vue3.0</title>
    <style>
        body,
        #app {
            text-align: center;
            padding: 30px;
        }
    </style>
    <script src="../../packages/vue/dist/vue.global.js"></script>
</head>
<body>
    <h3>computed</h3>
    <div id='app'></div>
</body>
<script>
    const { createApp, reactive, ref, computed } = Vue
    const App = {
        template: `
            <button @click='handleClick'>count++</button> 
            <div style="margin-top: 20px">{{ count }}</div>
        `,
        setup() {
            const refData = ref(0);

            const count = computed(()=>{
                return refData.value; 
            })

            const handleClick = () =>{
                refData.value += 1 // 要修改 count 的依赖项 refData
            }

            console.log("refData:" , refData)

            return {
                count,
                handleClick
            }
        }
    }
    createApp(App).mount('#app')
</script>
</html>

    <html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Hello Vue3.0</title>
    <style>
        body,
        #app {
            text-align: center;
            padding: 30px;
        }
    </style>
    <script src="../../packages/vue/dist/vue.global.js"></script>
</head>
<body>
    <h3>computed</h3>
    <div id='app'></div>
</body>
<script>
    const { createApp, reactive, ref, computed } = Vue
    const App = {
        template: `
            <button @click='handleClick'>count++</button> 
            <div style="margin-top: 20px">{{ count }}</div>
        `,
        setup() {
            const refData = ref(0);

            const count = computed({
                get(){
                    return refData.value;
                },
                set(value){
                    console.log("value:", value)
                    refData.value = value; 
                }
            })

            const handleClick = () =>{
                count.value += 1 // 直接修改 count
            }

            console.log(refData)

            return {
                count, 
                handleClick
            }
        }
    }
    createApp(App).mount('#app')
</script>
</html>

    watch & watchEffect

    watch : 创建 watch 监听

    watchEffect : 如果响应性的属性有变更，就会触发这个函数

    <html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Hello Vue3.0</title>
    <style>
        body,
        #app {
            text-align: center;
            padding: 30px;
        }
    </style>
    <script src="../../packages/vue/dist/vue.global.js"></script>
</head>
<body>
    <h3>watch && watchEffect</h3>
    <div id='app'></div>
</body>
<script>
    const { createApp, reactive, ref, watch, watchEffect } = Vue
    const App = {
        template: `
            <div class="container">
                <button style="margin-left: 10px" @click="handleClick()">按钮</button>
                <button style="margin-left: 10px" @click="handleStop">停止 watch</button>
                <button style="margin-left: 10px" @click="handleStopWatchEffect">停止 watchEffect</button>
                <div style="margin-top: 20px">{{ refData }}</div>
            </div>`
        ,
        setup() {
            let refData = ref(0);

            const handleClick = () =>{
                refData.value += 1
            }

            const stop = watch(refData, (val, oldVal) => {
                console.log('watch ', refData.value)
            })

            const stopWatchEffect = watchEffect(() => {
                console.log('watchEffect ', refData.value)
            })

            const handleStop = () =>{
                stop()
            }

            const handleStopWatchEffect = () =>{
                stopWatchEffect()
            }

            return {
                refData, 
                handleClick,
                handleStop,
                handleStopWatchEffect
            }
        }
    }
    createApp(App).mount('#app')
</script>
</html>

    v-model

    v-model：就是双向绑定
    <html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Hello Vue3.0</title>
    <style>
        body,
        #app {
            text-align: center;
            padding: 30px;
        }
    </style>
    <script src="../../packages/vue/dist/vue.global.js"></script>
</head>
<body>
    <h3>v-model</h3>
    <div id='app'></div>
</body>
<script>
    const { createApp, reactive, watchEffect } = Vue
    const App = {
        template: `<button @click='click'>reverse</button> 
                    <div></div>
                    <input v-model="state.message" style="margin-top: 20px" />
                    <div style="margin-top: 20px">{{ state.message }}</div>`,
        setup() {
            const state = reactive({
                message:'Hello Vue 3!!'
            })

            watchEffect(() => {
                console.log('state change ', state.message)
            })

            click = () => {
                state.message = state.message.split('').reverse().join('')
            }

            return {
                state,
                click
            }
        }
    }
    createApp(App).mount('#app')
</script>
</html>

    readonly

    使用 readonly 函数，可以把 普通 object 对象、reactive 对象、ref 对象 返回一个只读对象。

    返回的 readonly 对象，一旦修改就会在 console 有 warning 警告。

    程序还是会照常运行，不会报错。

    <html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Hello Vue3.0</title>
    <style>
        body,
        #app {
            text-align: center;
            padding: 30px;
        }
    </style>
    <script src="../../packages/vue/dist/vue.global.js"></script>
</head>
<body>
    <h3>readonly</h3>
    <div id='app'></div>
</body>
<script>
    const { createApp, reactive, readonly, watchEffect } = Vue
    const App = {
        template: `
            <button @click='click'>reverse</button> 
            <button @click='clickReadonly' style="margin-left: 20px">readonly++</button> 
            <div style="margin-top: 20px">{{ original.count }}</div>
        `,
        setup() {
            const original = reactive({ count: 0 })

            const copy = readonly(original)

            watchEffect(() => {
                // works for reactivity tracking
                console.log(copy.count)
            })

            click = () => {
                // mutating original will trigger watchers relying on the copy
                original.count++
            }

            clickReadonly = () => {
                // mutating the copy will fail and result in a warning
                copy.count++ // warning!
            }

            return {
                original,
                click,
                clickReadonly
            }
        }
    }
    createApp(App).mount('#app')
</script>
</html>

    provide & inject

    provide 和 inject 启用类似于 2.x provide / inject 选项的依赖项注入。

    两者都只能在 setup() 当前活动实例期间调用。

    import { provide, inject } from 'vue'

const ThemeSymbol = Symbol()

const Ancestor = {
  setup() {
    provide(ThemeSymbol, 'dark')
  }
}

const Descendent = {
  setup() {
    const theme = inject(ThemeSymbol, 'light' /* optional default value */)
    return {
      theme
    }
  }
}

    inject 接受可选的默认值作为第二个参数。

    如果未提供默认值，并且在 Provide 上下文中找不到该属性，则 inject 返回 undefined。

    Lifecycle Hooks

    Vue2 与 Vue3 的生命周期勾子对比：

    | Vue2 | Vue3 |
    | :------ | :------ |
    | beforeCreate | setup(替代) |
    | created | setup(替代) |
    | beforeMount | onBeforeMount |
    | mounted | onMounted |
    | beforeUpdate | onBeforeUpdate |
    | updated | onUpdated |
    | beforeDestroy | onBeforeUnmount |
    | destroyed | onUnmounted |
    | errorCaptured | onErrorCaptured |
    | 空 | onRenderTracked |
    | 空 | onRenderTriggered |

    除了 2.x 生命周期等效项之外，Composition API 还提供了以下调试挂钩：

    • onRenderTracked
    • onRenderTriggered

    这两个钩子都收到一个 DebuggerEvent，类似于观察者的 onTrack 和 onTrigger 选项：

    export default {
  onRenderTriggered(e) {
    debugger
    // inspect which dependency is causing the component to re-render
  }
}

    例子：

    <html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Hello Vue3.0</title>
    <style>
        body,
        #app {
            text-align: center;
            padding: 30px;
        }
    </style>
    <script src="../../packages/vue/dist/vue.global.js"></script>
</head>
<body>
    <h3>Lifecycle Hooks</h3>
    <div id='app'></div>
</body>
<script>
    const { createApp, reactive, onMounted, onUpdated, onUnmounted } = Vue
    const App = {
        template: `
            <div class="container">
                <button @click='click'>reverse</button>
                <div style="margin-top: 20px">{{ state.message }}</div>
            </div>`
        ,
        setup() {
            console.log('setup!')

            const state = reactive({
                message: 'Hello Vue3!!'
            })

            click = () => {
                state.message = state.message.split('').reverse().join('')
            }

            onMounted(() => {
                console.log('mounted!')
            })
            onUpdated(() => {
                console.log('updated!')
            })
            onUnmounted(() => {
                console.log('unmounted!')
            })

            return {
                state,
                click
            }
        }
    }
    createApp(App).mount('#app')
</script>
</html>

    最后

    本文只列出了笔者觉得会用得非常多的 api，Vue3.0 里面还有不少新特性的，比如 customRef、markRaw ，如果读者有兴趣可看 Vue Composition API 文档。

    参考文章：

    推荐阅读：

    1. 重磅：GitHub 上 100K+ Star 的前端面试开源项目汇总（进大厂必备）

    1. 强烈推荐: GitHub 上 170K+ Star 的前端学习的数据结构与算法项目
    2. 一张图理清Vue 3.0的响应式系统，实现精简版的响应式系统
    3. 黑学习方式：GitHub 上能挖矿的神仙技巧 - 如何发现优秀开源项目

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