Express.js Backend Guide

A practical guide to building production-ready Express.js applications with TypeScript.

🎯 What You'll Learn

• Server Architecture - Structured Express app with middleware
• Error Handling - Centralized error handling with proper logging
• Authentication - Protect routes with Better Auth
• Validation - Type-safe request validation with Zod
• Database - Drizzle ORM for type-safe database queries
• Logging - Winston logger setup for debugging and monitoring

📚 Sections

1. Server Setup

Learn how to structure an Express server with CORS, middleware, and routers.

2. Error Handling

Centralized error handling, status codes, and logging errors.

3. Authentication

Protect routes, check roles, and handle sessions with Better Auth.

4. Request Validation

Validate req.body, req.query, and req.params with Zod schemas.

5. Complete Request Flow

See how a complete request flows through middleware, validation, auth, controller, and database.

🚀 Quick Start

# Install dependencies
npm install express cors morgan http-status-codes
npm install -D @types/express @types/cors @types/morgan

# TypeScript & validation
npm install typescript zod
npm install -D ts-node

# Logging
npm install winston

# Database (optional)
npm install drizzle-orm postgres

📖 Basic Example

import express from "express";
import type { Request, Response } from "express";

const app = express();

// Middleware
app.use(express.json());

// Routes
app.get("/api/users", (req: Request, res: Response) => {
  res.json({ users: [] });
});

// Start server
app.listen(3000, () => {
  console.log("Server running on http://localhost:3000");
});

🎓 Core Concepts

Status Codes (http-status-codes)

import { StatusCodes } from "http-status-codes";

res.status(StatusCodes.OK).json({ data });              // 200
res.status(StatusCodes.CREATED).json({ user });         // 201
res.status(StatusCodes.BAD_REQUEST).json({ error });    // 400
res.status(StatusCodes.UNAUTHORIZED).json({ error });   // 401
res.status(StatusCodes.FORBIDDEN).json({ error });      // 403
res.status(StatusCodes.NOT_FOUND).json({ error });      // 404
res.status(StatusCodes.CONFLICT).json({ error });       // 409
res.status(StatusCodes.INTERNAL_SERVER_ERROR).json({}); // 500

Type Imports

import type { Request, Response, NextFunction } from "express";

Environment Variables

import "dotenv/config"; // Loads .env file automatically

Export Patterns

Feature	export default	named export
Number allowed	Only 1	Many
Import style	import x from	import { x } from
Renaming	Easy: import whatever from	Must rename: import { x as y }
Common use	Configs, single classes	Utils, services, constants

🛠️ Helper Functions

// Get client IP (handles proxies)
export function getClientIp(req: Request): string {
  if (req.headers["x-forwarded-for"]) {
    return (req.headers["x-forwarded-for"] as string).split(",")[0]!.trim();
  }
  if (req.headers["x-real-ip"]) {
    return req.headers["x-real-ip"] as string;
  }
  return req.ip!;
}

// Create URL-friendly slug
export function createSlug(title: string): string {
  return title
    .toLowerCase()
    .trim()
    .replace(/[^\w\s-]/g, "")
    .replace(/\s+/g, "-")
    .replace(/-+/g, "-");
}

// Generate random string
export function randString(): string {
  return crypto.randomBytes(20).toString("hex");
}

// Common API responses
export const commonResps = {
  internalError: {
    error: "Failed to complete request due to internal error",
    code: "internal_server_error",
  },
};

TypeScript Patterns

Type Assertion

const value as string  // Tells TS this is guaranteed to be a string

Filter Undefined Values

export function filterUndefined<T>(obj: T): {
  [K in keyof T]: Exclude<T[K], undefined>;
} {
  const result = {} as any;
  for (const key in obj) {
    if (obj[key] !== undefined) {
      result[key] = obj[key];
    }
  }
  return result;
}

Ignore TypeScript Errors (use sparingly!)

// @ts-ignore
const x: number = "this is actually a string";

📋 Next Steps

Start with Server Setup to build your Express application structure, then move through each section to add functionality.

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Pro Tip: Follow the request flow diagram in the Complete Request Flow section to understand how all pieces work together.