NodeJS

https://nodejs.org/en/learn
https://nodejs.org/api/
https://nodejs.org/api/esm.html
https://nodejs.org/api/test.html
https://nodejs.org/api/process.html
https://docs.npmjs.com/cli/v11/configuring-npm/package-json
https://eslint.org/docs/latest/use/getting-started

Node.js 是 JavaScript runtime:
    built on V8
    event loop / non-blocking IO
    good for API / worker / CLI / realtime apps
    ecosystem uses npm packages

适合:
    HTTP API
    BFF / gateway
    queue worker
    CLI tool
    realtime websocket service
    serverless function

不适合:
    CPU-heavy compute without worker thread / native addon
    blocking sync IO in hot path
    unbounded memory workload

核心原则:
    use Node.js LTS
    use ESM for new projects
    one package manager per project
    use npm ci in CI
    validate external input
    reuse clients and connection pools
    log structured JSON in production

mental model:
    JavaScript code
        -> Node.js runtime
        -> event loop handles async IO
        -> libuv handles many OS async operations
        -> npm manages packages

recommended:
    Node.js LTS
    npm bundled with Node.js

check:
    node -v
    npm -v

mkdir order-api
cd order-api

npm init -y

npm install express dotenv zod pino
npm install -D eslint @eslint/js globals vitest

dependencies:
    express:
        HTTP server framework

    dotenv:
        local .env loading

    zod:
        runtime validation

    pino:
        structured JSON logger

order-api
├── package.json
├── eslint.config.mjs
├── .env.example
├── .env.local
├── src
│   ├── main.js
│   ├── app.js
│   ├── config
│   │   └── config.js
│   ├── logger
│   │   └── logger.js
│   ├── errors
│   │   └── AppError.js
│   ├── orders
│   │   ├── OrderRepository.js
│   │   ├── OrderService.js
│   │   └── OrderRoutes.js
│   └── shared
│       └── result.js
└── test
    └── OrderService.test.js

structure rules:
    main.js:
        process entrypoint

    app.js:
        express app composition

    config/:
        environment config loading and validation

    logger/:
        logger singleton / factory

    errors/:
        application errors

    feature folder:
        repository
        service
        routes/controller

{
  "name": "order-api",
  "version": "1.0.0",
  "type": "module",
  "private": true,
  "scripts": {
    "dev": "node --watch src/main.js",
    "start": "node src/main.js",
    "test": "node --test",
    "lint": "eslint .",
    "lint:fix": "eslint . --fix",
    "check": "npm run lint && npm test"
  },
  "dependencies": {
    "dotenv": "latest",
    "express": "latest",
    "pino": "latest",
    "zod": "latest"
  },
  "devDependencies": {
    "@eslint/js": "latest",
    "eslint": "latest",
    "globals": "latest",
    "vitest": "latest"
  }
}

important:
    type=module:
        use ESM import/export

    private=true:
        prevents accidental npm publish

    package-lock.json:
        commit it
        use npm ci in CI

// createOrderId.js
import { randomUUID } from "node:crypto";

export function createOrderId() {
  return `o-${randomUUID()}`;
}

import { createOrderId } from "./createOrderId.js";

ESM note:
    local import path should include .js extension

const orderId = "o-1001";
let status = "PENDING";

status = "PAID";

rule:
    use const by default
    use let only when reassignment is needed
    avoid var

const order = {
  orderId: "o-1001",
  userId: "u-1001",
  amount: 99.9,
  status: "PENDING"
};

const items = [
  { sku: "sku-1001", quantity: 1 },
  { sku: "sku-1002", quantity: 2 }
];

const { orderId, userId } = order;

const paidOrder = {
  ...order,
  status: "PAID",
  paidAt: new Date().toISOString()
};

function calculateTotal(items) {
  return items.reduce((sum, item) => sum + item.quantity * item.price, 0);
}

const isPaid = (order) => order.status === "PAID";

async function findOrder(orderId) {
  return orderRepository.findById(orderId);
}

export class OrderService {
  constructor(repository) {
    this.repository = repository;
  }

  async markPaid(orderId) {
    const order = await this.repository.findById(orderId);

    if (order === null) {
      throw new Error("order not found");
    }

    return this.repository.save({
      ...order,
      status: "PAID"
    });
  }
}

import { readFile } from "node:fs/promises";
import { createServer } from "node:http";
import { randomUUID } from "node:crypto";

rule:
    use node: prefix for Node.js built-in modules

export class AppError extends Error {
  constructor(message, code, statusCode) {
    super(message);
    this.name = "AppError";
    this.code = code;
    this.statusCode = statusCode;
  }
}

export class OrderService {
  constructor(repository) {
    this.repository = repository;
  }

  async markPaid(orderId) {
    const order = await this.repository.findById(orderId);

    if (order === null) {
      throw new AppError("order not found", "ORDER_NOT_FOUND", 404);
    }

    if (order.status !== "PENDING") {
      throw new AppError("order status is not pending", "INVALID_ORDER_STATUS", 409);
    }

    return this.repository.save({
      ...order,
      status: "PAID",
      paidAt: new Date().toISOString()
    });
  }
}

rules:
    expected business error -> AppError
    unexpected error -> log stack and return generic 500
    never expose raw stack to client

import test from "node:test";
import assert from "node:assert/strict";

test("marks pending order as paid", async () => {
  const repository = new InMemoryOrderRepository([
    {
      orderId: "o-1001",
      userId: "u-1001",
      amount: 99.9,
      status: "PENDING"
    }
  ]);

  const service = new OrderService(repository);
  const order = await service.markPaid("o-1001");

  assert.equal(order.status, "PAID");
});

npm test

what to test:
    service business logic
    validation
    repository
    HTTP routes
    error mapping

npm install -D eslint @eslint/js

import eslint from "@eslint/js";
import globals from "globals";

export default [
  {
    ignores: [
      "node_modules/**",
      "coverage/**",
      "dist/**"
    ]
  },
  eslint.configs.recommended,
  {
    files: ["src/**/*.js", "test/**/*.js"],
    languageOptions: {
      ecmaVersion: "latest",
      sourceType: "module",
      globals: {
        ...globals.node
      }
    },
    rules: {
      "no-unused-vars": [
        "warn",
        {
          "argsIgnorePattern": "^_",
          "varsIgnorePattern": "^_"
        }
      ],
      "no-console": "off"
    }
  }
];

npm run lint
npm run lint:fix

lint vs test:
    lint:
        catches code quality and common mistakes

    test:
        checks behavior

config organization:
    .env.example
        committed template

    .env.local
        local development
        not committed

    .env.test
        test defaults

    staging / prod:
        injected by deployment platform

import "dotenv/config";
import { z } from "zod";

const configSchema = z.object({
  NODE_ENV: z.enum(["local", "dev", "test", "staging", "prod"]).default("local"),
  PORT: z.coerce.number().int().positive().default(3000),
  LOG_LEVEL: z.enum(["trace", "debug", "info", "warn", "error"]).default("info"),
  DATABASE_URL: z.string().url(),
  PAYMENT_API_URL: z.string().url()
});

const parsed = configSchema.safeParse(process.env);

if (!parsed.success) {
  console.error(parsed.error.flatten().fieldErrors);
  process.exit(1);
}

export const config = {
  env: parsed.data.NODE_ENV,
  port: parsed.data.PORT,
  logLevel: parsed.data.LOG_LEVEL,
  databaseUrl: parsed.data.DATABASE_URL,
  paymentApiUrl: parsed.data.PAYMENT_API_URL
};

import pino from "pino";
import { config } from "../config/config.js";

export const logger = pino({
  level: config.logLevel,
  base: {
    service: "order-api",
    env: config.env
  }
});

rules:
    JSON logs in production
    pretty logs only local
    include request_id / trace_id
    redact secrets

npm run dev

npm test

npm run lint

npm run start

node --inspect-brk src/main.js

production:
    run with NODE_ENV=production
    use process manager or container orchestrator
    configure graceful shutdown

export class InMemoryOrderRepository {
  constructor(initialOrders = []) {
    this.orders = new Map();

    for (const order of initialOrders) {
      this.orders.set(order.orderId, order);
    }
  }

  async findById(orderId) {
    return this.orders.get(orderId) ?? null;
  }

  async save(order) {
    this.orders.set(order.orderId, order);
    return order;
  }
}

import { randomUUID } from "node:crypto";

export class OrderService {
  constructor(repository) {
    this.repository = repository;
  }

  async createOrder(input) {
    const order = {
      orderId: randomUUID(),
      userId: input.userId,
      amount: input.amount,
      status: "PENDING",
      createdAt: new Date().toISOString()
    };

    return this.repository.save(order);
  }
}

import { Router } from "express";
import { z } from "zod";

export function createOrderRouter(orderService) {
  const router = Router();

  router.post("/orders", async (req, res, next) => {
    try {
      const input = z.object({
        userId: z.string().min(1),
        amount: z.number().positive()
      }).parse(req.body);

      const order = await orderService.createOrder(input);
      res.status(201).json(order);
    } catch (error) {
      next(error);
    }
  });

  return router;
}

import express from "express";
import { z } from "zod";
import { randomUUID } from "node:crypto";

const orders = new Map();

export function createApp() {
  const app = express();
  app.use(express.json());

  app.post("/orders", (req, res) => {
    const input = z.object({
      userId: z.string().min(1),
      amount: z.number().positive()
    }).parse(req.body);

    const order = {
      orderId: randomUUID(),
      userId: input.userId,
      amount: input.amount,
      status: "PENDING",
      createdAt: new Date().toISOString()
    };

    orders.set(order.orderId, order);
    res.status(201).json(order);
  });

  app.get("/orders/:orderId", (req, res) => {
    const order = orders.get(req.params.orderId);

    if (order === undefined) {
      res.status(404).json({
        error: {
          code: "ORDER_NOT_FOUND",
          message: "order not found"
        }
      });
      return;
    }

    res.json(order);
  });

  return app;
}

import { createApp } from "./app.js";

const port = Number(process.env.PORT ?? 3000);
const app = createApp();

app.listen(port, () => {
  console.log(`order-api listening on port ${port}`);
});

npm run dev

curl -s -X POST http://localhost:3000/orders -H 'content-type: application/json' -d '{"userId":"u-1001","amount":99.9}'

project:
    Node.js LTS
    ESM project
    package-lock.json committed
    npm ci in CI
    lint/test in CI

config:
    env config validated at startup
    secrets not committed
    production config injected by platform

code:
    external input validated
    async errors handled
    clients reused
    no sync IO in hot path
    no CPU-heavy work on event loop

runtime:
    structured logging
    request id / trace id
    health check endpoint
    graceful shutdown
    NODE_OPTIONS reviewed