How to let child components modify parent component data in Vue-JS Tutorial-php.cn

##1. Understanding watch in vue

If we want to monitor changes in an attribute, we use watch, usually when a parent component passes it to a child component

•1. Common usage scenarios

... watch:{ value(val) { console.log(val); this.visible = val; } } ...

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•2. If you want to execute it from the beginning

... watch: { firstName: { handler(newName, oldName) { this.fullName = newName + '-' + this.lastName; }, immediate: true, } } ...

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•3. Deep monitoring (array, object)

... watch: { obj: { handler(newName, oldName) { console.log('///') }, immediate: true, deep: true, } ...

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2. Understanding how to modify the properties of parent components in sub-components

After vue2.0 It is no longer a two-way binding. If you want to perform two-way binding, special processing is required.

[Vue warn]: Avoid mutating a prop directly since the value will be overwritten whenever the parent component re-renders. Instead, use a data or computed property based on the prop's value. Prop being mutated: "You Modified attribute name"

•1. Send the event to the parent component to modify

**在子组件test1中**   {{item}}
 ... methods: { add() { // 直接把数据发送给父组件 this.$emit('update', this.book); this.book = ''; }, }, **在父组件中**  ... addBook(val) { this.books = new Array(val) },

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•2. Use .sync to let the child component modify the parent The value of the component (actually a simplified version of the above method)

**在父组件中,直接在需要传递的属性后面加上.sync**  **在子组件中**

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•3. Copy a copy in the subcomponent

**子组件中** export default { props: { // 已经选中的 checkModalGroup: { type: Array, default: [], required: false, } }, data() { return{ copyCheckModalGroup: this.checkModalGroup, // 选中的 } }, methods: { // 一个一个的选择 checkAllGroupChange(data) { // 把当前的发送给父组件 this.$emit('updata', data); }, }, watch: { checkModalGroup(newVal, oldVal) { this.copyCheckModalGroup = newVal; } } } **父组件中直接更新传递给子组件的数据就可以** ... // 更新子组件数据 roleCheckUpdata(data) { this.roleGroup = data; }, ...

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