經過10個實例小練習，快速入門熟練 Vue3.0 核心新特性

時間  2020-05-12
標籤 經過 實例 練習 快速 入門 熟練 vue3.0 vue 核心 特性 简体版
原文   原文鏈接

Vue3.0 發 beta 版都有一段時間了，正式版也不遠了，因此真的要學習一下 Vue3.0 的語法了。html

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

環境搭建

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

下載完成以後打開代碼， 開啓 sourceMap :vue

  • tsconfig.json 把 sourceMap 字段修改成 true: "sourceMap": true
  • rollup.config.js 在 rollup.config.js 中，手動鍵入： output.sourcemap = true
  • 生成 vue 全局的文件：yarn dev
  • 在根目錄建立一個 demo 目錄用於存放示例代碼，並在 demo 目錄下建立 html 文件，引入構建後的 vue 文件

api 的使用都是很簡單的，下文的內容，看例子代碼就能懂了的，因此下面的例子不會作過多解釋。react

reactive

reactive: 建立響應式數據對象

setup 函數是個新的入口函數，至關於 vue2.x 中 beforeCreate 和 created，在 beforeCreate 以後 created 以前執行。git

<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 : 建立一個響應式的數據對象
isRef : 檢查值是不是 ref 的引用對象。 
<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

            // 判斷某值是不是響應式類型
            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 時，反應性引用和模板引用的概念是統一的。github

爲了得到對模板中元素或組件實例的引用，咱們能夠像往常同樣聲明 ref 並從 setup() 返回。面試

<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 : 將響應式數據對象轉換爲單一響應式對象

將一個 reactive 代理對象打平，轉換爲 ref 代理對象，使得對象的屬性能夠直接在 template 上使用。算法

<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 : 建立計算屬性 
<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 的依賴項 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 : 建立 watch 監聽

watchEffect : 若是響應性的屬性有變動，就會觸發這個函數json

<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()">按鈕</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>

v-model

v-model：就是雙向綁定 
<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 函數，能夠把 普通 object 對象、reactive 對象、ref 對象 返回一個只讀對象。api

返回的 readonly 對象，一旦修改就會在 console 有 warning 警告。

程序仍是會照常運行，不會報錯。

<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 啓用相似於 2.x provide / inject 選項的依賴項注入。

二者都只能在 setup() 當前活動實例期間調用。

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 接受可選的默認值做爲第二個參數。

若是未提供默認值，而且在 Provide 上下文中找不到該屬性，則 inject 返回 undefined。

Lifecycle Hooks

Vue2 與 Vue3 的生命週期勾子對比：

| 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 生命週期等效項以外，Composition API 還提供瞭如下調試掛鉤：

  • onRenderTracked
  • onRenderTriggered

這兩個鉤子都收到一個 DebuggerEvent，相似於觀察者的 onTrack 和 onTrigger 選項：

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>

最後

本文只列出了筆者以爲會用得很是多的 api，Vue3.0 裏面還有很多新特性的，好比 customRef、markRaw ，若是讀者有興趣可看 Vue Composition API 文檔。

參考文章：

推薦閱讀：

1. 重磅：GitHub 上 100K+ Star 的前端面試開源項目彙總（進大廠必備）

  1. 強烈推薦: GitHub 上 170K+ Star 的前端學習的數據結構與算法項目
  2. 一張圖理清Vue 3.0的響應式系統，實現精簡版的響應式系統
  3. 黑學習方式：GitHub 上能挖礦的神仙技巧 - 如何發現優秀開源項目

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