Chapter 7: Popular Libraries

1. lodash — Utility Library

npm install lodash
npm install -D @types/lodash

import _ from "lodash";

// pick / omit —— 提取或排除对象属性
const user = { id: 1, name: "Alice", password: "secret", role: "admin" };
const safe = _.omit(user, ["password"]); // { id, name, role }
const brief = _.pick(user, ["id", "name"]); // { id, name }

// debounce —— 防抖（常用于搜索输入）
const search = _.debounce((query: string) => {
    console.log("搜索:", query);
}, 300);

// cloneDeep —— 深拷贝（比 structuredClone 兼容性更好）
const original = { a: { b: [1, 2, 3] } };
const copy = _.cloneDeep(original);

// groupBy —— 分组
const orders = [
    { product: "手机", category: "电子" },
    { product: "耳机", category: "电子" },
    { product: "T恤", category: "服装" },
];
const grouped = _.groupBy(orders, "category");
// { "电子": [...], "服装": [...] }

Tip: If only using a few functions, consider lodash-es with tree-shaking to reduce bundle size.

2. dayjs — Date Handling

dayjs is a lightweight replacement for moment.js (only 2KB), with an almost fully compatible API.

npm install dayjs

import dayjs from "dayjs";
import relativeTime from "dayjs/plugin/relativeTime";
import "dayjs/locale/zh-cn";

dayjs.extend(relativeTime);
dayjs.locale("zh-cn");

// 解析与格式化
const now = dayjs();
console.log(now.format("YYYY-MM-DD HH:mm:ss")); // "2026-03-30 14:30:00"

// 日期操作
const nextWeek = now.add(7, "day");
const lastMonth = now.subtract(1, "month");

// 相对时间（需要 relativeTime 插件）
console.log(dayjs("2026-03-28").fromNow()); // "2 天前"

// 比较
const deadline = dayjs("2026-04-15");
console.log(deadline.isAfter(now)); // true
console.log(deadline.diff(now, "day")); // 16

3. zod — Runtime Data Validation

zod validates data structures at runtime and automatically infers TypeScript types — define once, use twice.

npm install zod

import { z } from "zod";

// 定义 schema
const CreateUserSchema = z.object({
    name: z.string().min(2).max(50),
    email: z.string().email(),
    age: z.number().int().min(0).max(150).optional(),
    role: z.enum(["admin", "user", "guest"]).default("user"),
});

// 自动推导类型（无需手写 interface）
type CreateUserInput = z.infer<typeof CreateUserSchema>;

// 验证外部数据
function handleCreateUser(rawBody: unknown): CreateUserInput {
    const result = CreateUserSchema.safeParse(rawBody);
    if (!result.success) {
        console.error("验证失败:", result.error.flatten());
        throw new Error("Invalid input");
    }
    return result.data; // 类型安全的 CreateUserInput
}

4. winston / pino — Logging Libraries

Production environments need structured logging. winston is feature-rich, pino pursues extreme performance.

npm install winston

import winston from "winston";

const logger = winston.createLogger({
    level: "info",
    format: winston.format.combine(
        winston.format.timestamp(),
        winston.format.json()
    ),
    transports: [
        new winston.transports.Console({
            format: winston.format.combine(
                winston.format.colorize(),
                winston.format.simple()
            ),
        }),
        new winston.transports.File({ filename: "logs/error.log", level: "error" }),
        new winston.transports.File({ filename: "logs/combined.log" }),
    ],
});

logger.info("服务已启动", { port: 3000 });
logger.error("数据库连接失败", { host: "localhost", error: "ECONNREFUSED" });

For high-performance scenarios, pino is recommended — JSON serialization is 5x+ faster than winston.

5. dotenv — Environment Variable Management

npm install dotenv

Create a .env file (add to .gitignore):

DATABASE_URL=postgresql://user:pass@localhost:5432/mydb
API_KEY=sk-xxxxxxxxxxxx
PORT=3000

import "dotenv/config"; // 在入口文件顶部导入

// 类型安全的环境变量读取
function getEnv(key: string): string {
    const value = process.env[key];
    if (!value) throw new Error(`缺少环境变量: ${key}`);
    return value;
}

const dbUrl = getEnv("DATABASE_URL");
const port = Number(getEnv("PORT"));

6. vitest — Testing Framework

vitest is compatible with Jest API but faster, with native TypeScript and ESM support.

npm install -D vitest

// math.ts
export function add(a: number, b: number): number { return a + b; }
export function divide(a: number, b: number): number {
    if (b === 0) throw new Error("除数不能为零");
    return a / b;
}

// math.test.ts
import { describe, it, expect } from "vitest";
import { add, divide } from "./math";

describe("math 模块", () => {
    it("add 正确相加", () => {
        expect(add(2, 3)).toBe(5);
        expect(add(-1, 1)).toBe(0);
    });

    it("divide 除零抛异常", () => {
        expect(() => divide(10, 0)).toThrow("除数不能为零");
    });
});

npx vitest        # 监听模式
npx vitest run    # 单次运行
npx vitest --coverage  # 覆盖率报告

7. commander — CLI Tool Building

npm install commander

import { Command } from "commander";

const program = new Command();

program
    .name("mytool")
    .version("1.0.0")
    .description("一个示例 CLI 工具");

program
    .command("greet <name>")
    .option("-l, --lang <language>", "语言", "zh")
    .description("向某人打招呼")
    .action((name: string, opts: { lang: string }) => {
        const msg = opts.lang === "zh" ? `你好，${name}！` : `Hello, ${name}!`;
        console.log(msg);
    });

program.parse(); // 解析 process.argv

npx ts-node cli.ts greet Alice --lang en
# Hello, Alice!

8. Framework Selection Reference

📝 Chapter Summary