How to Create an Express Server From Scratch

How to Create an Express Server From Scratch

Creating an Express server is the first real step of a Node.js backend. Here is the step-by-step guide.

Step 1: Initialize the Project

Run npm init -y in an empty folder. This creates package.json with defaults.

Step 2: Install Express

Run npm install express. This adds Express to your dependencies.

Step 3: Install Dev Dependencies

Run npm install --save-dev nodemon. nodemon restarts the server on file changes. Add a dev script: "dev": "nodemon src/server.js".

Step 4: Create the Server File

Create src/server.js:

const express = require('express');
const app = express();

app.get('/health', (req, res) => {
  res.status(200).json({ status: 'ok' });
});

const PORT = process.env.PORT || 3000;
app.listen(PORT, () => {
  console.log(`Server running on port ${PORT}`);
});

Step 5: Add JSON Body Parsing

Add app.use(express.json()) before your routes. This lets you read JSON bodies from POST requests. Without it, req.body is undefined.

Step 6: Add Cor

Run npm install cors and add app.use(cors()) if your client and server are on different origins. Skip this if same origin.

Step 7: Add Environment Variables

Run npm install dotenv. Create a .env file with PORT=3000. Add require('dotenv').config() at the top of server.js. Add .env to .gitignore.

Step 8: Run the Server

Run npm run dev. Visit http://localhost:3000/health. You should see { "status": "ok" }.

Step 9: Add a Health Check

You already added /health. Keep it. It is useful for uptime monitors, load balancers, and CI checks.

Step 10: Add an Error Handler

At the bottom of server.js (after all routes), add an error-handling middleware:

app.use((err, req, res, next) => {
  console.error(err.stack);
  res.status(500).json({ error: 'Something went wrong' });
});

The Takeaway

Create an Express server by initializing the project, installing Express and nodemon, creating server.js with a health check route, adding JSON body parsing, CORS (if cross-origin), dotenv for env vars, and an error-handling middleware. Run with npm run dev and confirm /health returns 200.