经过10个实例小练习，快速熟练 Vue3.0 核心新特性

时间 2020-05-14

标签经过实例练习快速熟练 vue3.0 vue 核心特性繁體版

原文原文链接

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

环境搭建

$ git pull https://github.com/vuejs/vue-next.git
$ cd vue-next && yarn
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下载完成以后打开代码，开启 sourceMap :html

tsconfig.json 把 sourceMap 字段修改成 true: "sourceMap": truevue
rollup.config.js 在 rollup.config.js 中，手动键入： output.sourcemap = truejava
生成 vue 全局的文件：yarn devreact
在根目录建立一个 demo 目录用于存放示例代码，并在 demo 目录下建立 html 文件，引入构建后的 vue 文件git

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，因此下面的例子不会作过多解释。github

reactive

reactive: 建立响应式数据对象json

setup 函数是个新的入口函数，至关于 vue2.x 中 beforeCreate 和 created，在 beforeCreate 以后 created 以前执行。api

<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>
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ref & isRef

ref : 建立一个响应式的数据对象 isRef : 检查值是不是 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 // 判断某值是不是响应式类型 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>
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Template Refs

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

为了得到对模板中元素或组件实例的引用，咱们能够像往常同样声明 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>
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<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>
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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，使得对象的属性能够直接在 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>
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computed

computed : 建立计算属性

<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>
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<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>
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watch & watchEffect

watch : 建立 watch 监听

watchEffect : 若是响应性的属性有变动，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">中止 watch</button> <button style="margin-left: 10px" @click="handleStopWatchEffect">中止 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>
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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>
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readonly

使用 readonly 函数，能够把普通 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。

程序仍是会照常运行，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>
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provide & inject

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

二者都只能在 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
    }
  }
}
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inject 接受可选的默认值做为第二个参数。

若是未提供默认值，而且在 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 生命周期等效项以外，Composition API 还提供了如下调试挂钩：

onRenderTracked
onRenderTriggered

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

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

GitHub 博客地址: github.com/biaochenxuy… 。

本文只列出了笔者以为会用得很是多的 api，Vue3.0 里面还有很多新特性的，好比 customRef、markRaw ，若是读者有兴趣可看 Vue Composition API 文档。

Vue Composition API 文档: composition-api.vuejs.org/api.html#se…
vue-next 地址: github.com/vuejs/vue-n…

参考文章：

Vue3 尝鲜