在SFC中支持声明式作用域 <declare></declare> (Support declarative scope in SFC)

[gme-gpl]

在SFC中支持声明式作用域 <declare></declare> (Support declarative scope in SFC)

当组件作为子组件接收父组件数据或触发父组件事件时, 我们使用 defineProps, defineEmits 以及最近新引入的 defineModel 宏. 但是受限于 javascript/typescipt 的约束, 这些宏在写法和功能上都有一些不足, 与其艰难地推动语法糖, 不如新创建一个 <declare></declare> 作用域概念来将父子组件之间的逻辑抽离出来, 提高代码的可读性.

When a component receives parent data as a child component or triggers parent events, we use defineProps, defineEmits and recently introduced defineModel macros. However, limited by the constraints of javascript/typescipt, these macros have some shortcomings in writing and functionality, and Instead of pushing grammar sugar with difficulty, it is better to create a new one <declare></declare> scope to extract logic between parent and child components, improving the readability of the code.

预期的效果(Expected effect)

子组件(Child Component)

<declare>
name: string       // 普通参数(normal parameter)
age: number = 20   // 带默认值的参数(parameter with default value)
// 类似于typescript的自动类型推导, 可以将其写为( similar to automatic type inference in TypeScript, It can be written as): `age := 20`

#gender: 'male' | 'female'  // v-model参数(v-model parameter)

@addYears(years: number)     // 父组件事件(emits)
</declare>

<script setup lang="ts">
import { watch, compute } from 'vue';

// 声明在<declare>中的`name`, 等同于: const name = ref<string>('<placeholder>')
// `name` declared in <declare>, is equivalent to: 
// const name: Readonly<Ref<number>> = ref('<placeholder>')
watch(name, () => console.log('name被修改了(name has be modified)')) 

const nextYearAge = compute(() => age.value+1)
</script>

<template>
  <h1>I'm {{ name.toUpperCase() }}, {{ age }} years old</h1>
  <h2>And I will be {{ nextYearAge }} years old next year</h2>
  <p>
    My gender is 
    <select v-model="modelValue">
      <option>male</option>
      <option>female</option>
    </select>
  </p>
  <button @click="addYears(10)">Add 10 years old</button>
</template>

父组件(Parent Component)

<script setup lang="ts">
import { ref } from 'vue';

const name = ref('my_name')
const age = ref(23)
const gender = ref<'male' | 'female'>('male')

function addYears(years: number) {
    age.value += years
}

</script>

<template>
    <ChildComponent :name="name" :age="age" v-model:gender="gender" @add-years="addYears" />
</template>

使用外部类型(Use External Type)

外部Typescript(External TypeScript)

export interace Person {
    name: string,
    age?: number,
    gender?: 'male' | 'female',
}

子组件(Child Component)

<declare>
import { Person } from './external.ts';

export Person {
    age := 20
}
</declare>

等同于(Equivalent to)

<declare>
name: string
age: number = 20
gender?: 'male' | 'female'
</declare>

一些考虑(FAQ)

问: 这种写法并不是标准的 typescript 语法, 使用者可能有心智负担

答: 确实会这样, 但是我觉得这种心智负担是可以接受的,

在 <template> 中使用插值表达式或vue指令, 也并不符合html语法规范, 但也是被接受的.
这种写法的语法和 typescript 相类似, 并不会造成很大的心智负担