TypeScript 进阶：泛型与工具类型详解

泛型基础

泛型让代码更灵活，同时保持类型安全。

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

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

泛型约束

interface Lengthwise {
  length: number;
}

function logLength<T extends Lengthwise>(arg: T): void {
  console.log(arg.length);
}

logLength("hello"); // ✅
logLength(123); // ❌

常用工具类型

Partial - 全部可选

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

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

Required - 全部必填

type RequiredUser = Required<PartialUser>;

Pick - 选择部分

type UserName = Pick<User, "name">;
// { name: string; }

Omit - 排除部分

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

Record - 键值映射

type RoleMap = Record<string, number>;

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];
};

掌握这些高级类型，让你的 TypeScript 代码更强大！