# NestJS — Progressive Node.js Framework for Enterprise Apps

> NestJS is a progressive Node.js framework for building efficient, scalable, and enterprise-grade server-side applications with TypeScript. It uses modular architecture inspired by Angular and supports Express/Fastify underneath.

## Install

Save in your project root:

## Quick Use

```bash
npm i -g @nestjs/cli
nest new project-name
cd project-name
npm run start:dev
```

Generate a resource:
```bash
nest g resource users
```

## Intro

NestJS is a framework for building efficient, scalable Node.js server-side applications. Built with TypeScript (fully supports vanilla JavaScript) and combines elements of OOP, FP, and FRP. Under the hood it uses Express by default but can swap to Fastify.

- **Repo**: https://github.com/nestjs/nest
- **Stars**: 75K+
- **Language**: TypeScript
- **License**: MIT

## What NestJS Does

Provides out-of-the-box architecture for testable, scalable, loosely-coupled, and maintainable backend apps:
- **Modules** — organize code by feature
- **Controllers** — handle incoming HTTP requests
- **Providers/Services** — business logic via dependency injection
- **Pipes/Guards/Interceptors** — cross-cutting concerns
- **Microservices** — Kafka, RabbitMQ, gRPC, Redis, NATS transport
- **GraphQL** — code-first or schema-first
- **WebSockets** — real-time gateways

## Architecture

Angular-inspired modular architecture: every app has a root `AppModule` that imports feature modules. Each feature module declares controllers and providers. DI container wires everything at startup.

```
AppModule
├── UsersModule (UsersController, UsersService)
├── AuthModule (AuthController, AuthService, JwtStrategy)
└── DatabaseModule (TypeOrmModule.forRoot)
```

## Self-Hosting

```bash
# Production build
npm run build
node dist/main.js

# Docker
FROM node:20-alpine
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production
COPY dist ./dist
CMD ["node", "dist/main.js"]
```

## Key Features

- TypeScript-first with decorators
- Built-in DI container
- Express or Fastify HTTP adapter
- OpenAPI/Swagger auto-generation
- TypeORM/Prisma/Mongoose integrations
- CLI for scaffolding
- Testing utilities (Jest-based)

## Comparison

| Framework | DI | TypeScript | Opinionated | Best For |
|---|---|---|---|---|
| NestJS | Built-in | First-class | Yes | Enterprise backends |
| Express | Manual | Optional | No | Minimal APIs |
| Fastify | Manual | Good | No | High-perf APIs |
| Koa | Manual | Optional | No | Middleware composition |

## 常见问题 FAQ

**Q: NestJS 和 Express 的关系？**
A: NestJS 默认使用 Express 作为 HTTP 层，但抽象了路由/中间件，提供更高层的模块/DI 架构。可以替换为 Fastify。

**Q: 性能怎么样？**
A: 使用 Fastify adapter 后性能接近原生 Fastify。默认 Express adapter 的开销来自抽象层。

**Q: 学习曲线陡吗？**
A: 如果熟悉 Angular 几乎零门槛；Express 用户需要理解装饰器和 DI。

## 来源与致谢 Sources

- Official Docs: https://docs.nestjs.com
- GitHub: https://github.com/nestjs/nest
- License: MIT

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Author: AI Open Source