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setup 函数的第二个参数 context 中包含 emit 方法

news 2026/5/14 16:15:38

在生产环境中，只声明 props 的名称是不够的。为了让组件更健壮，你需要为 props 指定类型、默认值甚至自定义验证函数。

props: {
// 基础类型检查
title: String,

// 必填项
price: {type: Number,required: true
},
http://www.baidu.com/link?url=UK9M1kYPo9nuMx1XaXo4eSngXtmNqc6y19LbKAnD_hBUHfvpc9EzrR5yzqyjJJbKRV8LOHFunrx_607wHRPVtK
// 带有默认值的对象
// 注意：对象或数组的默认值必须从一个工厂函数返回
config: {type: Object,default(rawProps) {return { theme: 'dark' }}
},// 自定义验证函数
status: {type: String,validator(value) {// 这个值必须匹配下列字符串中的一个return ['success', 'warning', 'danger'].includes(value)}
}

}

2.3 命名规范

在 JavaScript 中：使用 camelCase (驼峰命名法)，例如 props.productName。

在 HTML 模板中：使用 kebab-case (短横线命名法)，例如。
Vue 会自动处理这两者之间的转换。

Emit：子传父 (Events Up)

既然子组件不能修改 props，那它想改变数据怎么办？（比如用户点击了子组件里的“删除”按钮）。
它必须通知父组件，请求父组件来执行修改。

3.1 触发与监听

触发：子组件使用 $emit('event-name', payload) 抛出一个事件。payload 是可选的参数，用于传递具体的数据。

监听：父组件像监听原生 DOM 事件（如 click）一样，使用 @event-name="handler" 监听这个自定义事件。

3.2 声明 Emits (Vue 3 推荐)

为了让组件的行为更清晰，Vue 3 建议我们在组件中显式声明它会抛出哪些事件。这不仅有助于文档化，还能让 Vue 自动校验事件。

// 声明该组件会触发的事件
emits: ['add-to-cart', 'delete-item'],
// 或者对象语法进行验证
emits: {
'add-to-cart': (id) => {
if (id) return true; // 验证通过
console.warn('add-to-cart 事件缺少 id 参数');
return false;
}
}

实战案例：购物车计数器

我们将构建一个简单的父子组件系统，演示完整的交互流程。

父组件 (App)：维护一个商品列表和总价。它是数据的“单一事实来源”。

子组件 (ProductItem)：展示单个商品，并包含“加入购物车”按钮。它只负责展示和通知。

我们将代码逻辑拆解为三个部分：

4.1 子组件逻辑 (ProductItem)

子组件负责声明它需要什么数据 (props)，验证这些数据，并在用户交互时发送通知 (emit)。

const ProductItem = {
// 1. 严格的 Props 声明
props: {
id: {
type: Number,
required: true
},
name: {
type: String,
required: true
},
price: {
type: Number,
required: true
}
},
// 2. 声明抛出的事件
emits: ['add-to-cart'],

// setup 函数的第二个参数 context 中包含 emit 方法
setup(props, { emit }) {const notifyParent = () => {// 核心：子组件不直接修改数据，而是发出通知// 我们把商品的 id 和 price 打包发给父组件
        // 这里的 { id: ..., price: ... } 就是 payload

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