keyof typeof 是什么意思
keyof 作用于 object 类型，并返回这个 object 的 key 的集合类型：
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type Point = { x: number; y: number };
type P = keyof Point; // type '"x" | "y"'
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typeof 操作符作用于 JavaScript 对象和作用于 TypeScript 类型的时候结果是不一样的：
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const obj = {
name: "aaa",
key: "bbb",
};
type ObjType = typeof obj;
// type ObjType = { name: string; key: string; }
const newObj: ObjType = {
name: 1111, // Type 'number' is not assignable to type 'string'.
};
console.log(typeof obj); // "object"
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所以 keyof typeof 就是获取 JavaScript 对象的 key 的集合。
几个内置类型
Record<Keys, Type>
创建一个 key 类型是 Keys，value 类型是 Type 的对象类型。
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interface CatInfo {
age: number;
breed: string;
}
type CatName = "miffy" | "boris" | "mordred";
const cats: Record<CatName, CatInfo> = {
miffy: { age: 10, breed: "Persian" },
boris: { age: 5, breed: "Maine Coon" },
mordred: { age: 16, breed: "British Shorthair" },
};
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ReturnType<Type>
返回函数 Type 的返回类型。
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type Fn = () => { a: number; b: number };
type Type1 = ReturnType<Fn>; // {a: number, b: number}
function fn() {
return { a: 1, b: 2 };
}
type Type2 = ReturnType<fn>; // fn refers to a value, but is being used as a type here. Did you mean 'typeof f'?
type Type2 = ReturnType<typeof fn>; // {a: number, b: number}
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参考资料