TypeScript 类型系统进阶

泛型基础

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

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

泛型约束

interface Lengthwise {
  length: number;
}

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

工具类型

Partial - 全部可选

interface User { id: number; name: string; }
type PartialUser = Partial<User>;

Pick - 选择属性

type UserPreview = Pick<User, "id" | "name">;

Omit - 排除属性

type UserWithoutId = Omit<User, "id">;

Record - 键值映射

type RoleMap = Record<string, number>;

条件类型

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

映射类型

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

掌握类型系统，让代码更安全可靠！