mkdir 03-composition-api
# 初始化项目package.json
npm init --yes
# 安装vue3
npm install vue@next --save
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reactive返回对象的响应式副本
<!-- 01-createApp.html --> <!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8" /> <meta http-equiv="X-UA-Compatible" content="IE=edge" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <title>createApp & reactive</title> </head> <body> <div id="app"> x: {{ position.x }}<br /> y: {{ position.y }} </div> <script type="module"> import { createApp, reactive, } from './node_modules/vue/dist/vue.esm-browser.js' const app = createApp({ setup() { // reactive用于设置对象响应式 const position = reactive({ x: 0, y: 0, }) return { position, } }, mounted() { this.position.x = 100 }, }) app.mount('#app') </script> </body> </html>可以将鼠标移动的相关的参数和方法统一封装在一个函数中，使用toRefs将响应式对象转换为普通对象
// 将鼠标移动相关统一放在一起 function useMousePosition() { const position = reactive({ x: 0, y: 0, }) const update = (e) => { position.x = e.pageX position.y = e.pageY } onMounted(() => { window.addEventListener('mousemove', update) }) onUnmounted(() => { window.removeEventListener('mousemove', update) }) // 返回时转换为ref return toRefs(position) }然后在 setup 函数中使用
setup() { // 通过toRefs可以在不失去响应性的情况下解构 const { x, y } = useMousePosition() return { x, y, } } -
ref 接受一个内部值并返回一个响应式且可变的 ref 对象
... <div id="app"> <button @click="increase">增加</button> <span>{{ count }}</span> </div> ... <script type="module"> function useRef() { const count = ref(0) return { count, increase: () => { // count.value++ }, } } const app = createApp({ setup() { return { ...useRef(), } }, }) </script> -
computed 接受一个 getter 函数，并为从 getter 返回的值返回一个不变的响应式 ref 对象
... <div id="app"> <button @click="push">按钮</button> 未完成：{{ activeCount }} </div> ... <script type="module"> const data = [ { text: '看书', completed: false }, { text: '敲代码', completed: false }, { text: '约会', completed: true }, ] createApp({ setup() { const todos = reactive(data) const activeCount = computed(() => { return todos.filter((item) => !item.completed).length }) return { activeCount, push: () => { todos.push({ text: '开会', completed: false, }) }, } }, }).mount('#app') </script> -
watch watch 与 Options API this.$watch(以及相应的 watch 选项) 完全等效
createApp({ setup() { const question = ref('') const answer = ref('') watch(question, async (newValue, oldValue) => { const response = await fetch('https://www.yesno.wtf/api') const data = await response.json() answer.value = data.answer }) return { question, answer, } }, }).mount('#app') -
watchEffect 在响应式地跟踪其依赖项时立即运行一个函数，并在更改依赖项时重新运行它
createApp({ setup() { const count = ref(0) const stop = watchEffect(() => { console.log(count.value) }) return { count, stop, increase: () => { count.value++ }, } }, }).mount('#app')
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