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高级打字脚本:查找嵌套对象中键“id”的所有值

recursion typescript

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David Alvarez · 技术社区 · 2 年前

我试图提取对象中第一层和所有嵌套层的键“id”的所有值。

鉴于我 ExampleType ,我想 NestedID<ExampleType> 成为 "one" | "two" | "three" | "four" 然而,我做错了什么,这只会让我 "one" 我不明白为什么。

有人明白为什么这行不通吗?

我的灵感来自 https://dev.to/pffigueiredo/typescript-utility-keyof-nested-object-2pa3 这是一个非常好的教程。

type ExampleType = {
  id: "one"
  children: [{ id: "two" }, { id: "three"; children: [{ id: "four" }] }, { abc: "def" }]
  efg: "hij"
}

type NestedId<ObjectType extends Record<string, any> | undefined> = {
  [Key in keyof ObjectType & string]: ObjectType[Key] extends undefined
    ? never
    : Key extends "id" // if the key is "id"
      ? ObjectType[Key] // return the value of the key
      : Key extends "children" // else, if the key is "children"
        ? ObjectType[Key] extends Array<Record<string, any> | undefined> // and its value is an array of object
          ? NestedId<ObjectType[Key][number]> // recursive call
          : never // else, children value is not an object --> return never
        : never // else, key is not "id" or "children" --> return never
}[keyof ObjectType & string]

const id1: NestedId<ExampleType> = "one" // works as expected
const id2: NestedId<ExampleType> = "two" // doesn't work (Type "two" is not assignable to type "one")
const id3: NestedId<ExampleType> = "three" // doesn't work (Type "three" is not assignable to type "one")
const id4: NestedId<ExampleType> = "four" // doesn't work (Type "four" is not assignable to type "one")
const foo: NestedId<ExampleType> = "foo" // works as expected
const bar: NestedId<ExampleType> = "bar" // works as expected

1 回复 | 直到 2 年前

1

braza 2 年前

您可以使用 infer 为了实现这一目标。它获取父id,并递归检查子props,以便从那里添加id(如果存在的话)。

type NestedId<ObjectType> = 
  ObjectType extends { id: infer IdType } 
    ? IdType | (ObjectType extends { children: Array<infer ChildType> } 
      ? NestedId<ChildType> 
      : never) 
    : never;

在这个例子中,你会得到 "one" | "two" | "three" | "four" 回来,其他一切都像 "foo" 将出错。