Node.js Backend Development with TypeScript

progressive_disclosure: entry_point: summary: "TypeScript backend patterns with Express/Fastify, routing, middleware, database integration" when_to_use: - "When building REST APIs with TypeScript" - "When creating Express/Fastify servers" - "When needing server-side TypeScript" - "When building microservices" quick_start: - "npm init -y && npm install -D typescript @types/node tsx" - "npm install express @types/express zod" - "Create tsconfig.json with strict mode" - "npm run dev" token_estimate: entry: 75 full: 4700

TypeScript Setup

Essential Configuration

tsconfig.json (strict mode recommended):

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "NodeNext",
    "moduleResolution": "NodeNext",
    "outDir": "./dist",
    "rootDir": "./src",
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true,
    "resolveJsonModule": true,
    "types": ["node"]
  },
  "include": ["src/**/*"],
  "exclude": ["node_modules", "dist"]
}

package.json scripts:

{
  "scripts": {
    "dev": "tsx watch src/server.ts",
    "build": "tsc",
    "start": "node dist/server.js",
    "test": "vitest"
  }
}

Development Dependencies

npm install -D typescript @types/node tsx vitest
npm install -D @types/express  # or @types/node (Fastify has built-in types)

Express Patterns

Basic Express Server

src/server.ts:

import express, { Request, Response, NextFunction } from 'express';
import { z } from 'zod';

const app = express();
const port = process.env.PORT || 3000;

// Middleware
app.use(express.json());
app.use(express.urlencoded({ extended: true }));

// Type-safe request handlers
interface TypedRequest<T> extends Request {
  body: T;
}

// Routes
app.get('/health', (req: Request, res: Response) => {
  res.json({ status: 'ok', timestamp: new Date().toISOString() });
});

// Start server
app.listen(port, () => {
  console.log(`Server running on port ${port}`);
});

Router Pattern

src/routes/users.ts:

import { Router } from 'express';
import { z } from 'zod';
import { validateRequest } from '../middleware/validation';

const router = Router();

const createUserSchema = z.object({
  email: z.string().email(),
  name: z.string().min(2),
  age: z.number().int().positive().optional(),
});

router.post(
  '/users',
  validateRequest(createUserSchema),
  async (req, res, next) => {
    try {
      const userData = req.body; // Type-safe after validation
      // Database insert logic
      res.status(201).json({ id: 1, ...userData });
    } catch (error) {
      next(error);
    }
  }
);

export default router;

Middleware Patterns

src/middleware/validation.ts:

import { Request, Response, NextFunction } from 'express';
import { z, ZodSchema } from 'zod';

export const validateRequest = (schema: ZodSchema) => {
  return (req: Request, res: Response, next: NextFunction) => {
    try {
      req.body = schema.parse(req.body);
      next();
    } catch (error) {
      if (error instanceof z.ZodError) {
        res.status(400).json({
          error: 'Validation failed',
          details: error.errors,
        });
      } else {
        next(error);
      }
    }
  };
};

src/middleware/auth.ts:

import { Request, Response, NextFunction } from 'express';