TypeScript 类型体操：高级类型技巧

泛型基础

function identity<T>(arg: T): T {
  return arg;
}

const result = identity<string>("hello");

实用工具类型

Partial - 全部可选

interface User {
  id: number;
  name: string;
  email: string;
}

type PartialUser = Partial<User>;
// { id?: number; name?: string; email?: string }

Pick - 选择部分

type UserPreview = Pick<User, "id" | "name">;
// { id: number; name: string }

Omit - 排除部分

type UserWithoutEmail = Omit<User, "email">;
// { id: number; name: string }

Record - 键值映射

type UserRole = "admin" | "user" | "guest";
const permissions: Record<UserRole, string[]> = {
  admin: ["read", "write", "delete"],
  user: ["read"],
  guest: []
};

条件类型

type IsString<T> = T extends string ? true : false;

type A = IsString<string>;  // true
type B = IsString<number>;  // false

映射类型

type Readonly<T> = {
  readonly [P in keyof T]: T[P];
};

type Nullable<T> = {
  [P in keyof T]: T[P] | null;
};

推断类型

type ReturnType<T> = T extends (...args: any[]) => infer R ? R : any;

function getUser() {
  return { id: 1, name: "张三" };
}

type User = ReturnType<typeof getUser>;

实战示例

// 深度 Readonly
type DeepReadonly<T> = {
  readonly [P in keyof T]: T[P] extends object ? DeepReadonly<T[P]> : T[P];
};

// 函数参数类型提取
type FirstParameter<T extends (...args: any[]) => any> = 
  T extends (first: infer P, ...rest: any[]) => any ? P : never;

掌握类型体操，让 TypeScript 成为你的得力助手！