Build Your First REST API With Node.js and Express in 30 Minutes

#api #express #backend #node

Introduction

A REST API is a way for a frontend, a mobile app, or another service to ask your server for data, and to send data back. Node.js with Express is a good first choice for learning APIs because the setup is small and the concepts transfer to other backend frameworks.

In this post, you will build a tiny users API with two routes: one to list users, and one to add a user.

Step 1: Set up the project

Create a folder, then run:

npm init -y
npm install express

Add this to your package.json so you can run the server easily:

{
  "scripts": {
    "start": "node index.js"
  }
}

Step 2: Create the server

Create a file called index.js:

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

app.use(express.json());

let users = [
  { id: 1, name: "Ali" },
  { id: 2, name: "Sara" },
];

// GET /users — list all users
app.get("/users", (req, res) => {
  res.json(users);
});

// GET /users/:id — get one user
app.get("/users/:id", (req, res) => {
  const user = users.find((u) => u.id === Number(req.params.id));
  if (!user) {
    return res.status(404).json({ error: "User not found" });
  }
  res.json(user);
});

// POST /users — add a user
app.post("/users", (req, res) => {
  const { name } = req.body;
  if (!name) {
    return res.status(400).json({ error: "Name is required" });
  }
  const newUser = { id: users.length + 1, name };
  users.push(newUser);
  res.status(201).json(newUser);
});

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

Run it with:

npm start

Then test it in a browser or with curl:

curl http://localhost:3000/users
curl -X POST http://localhost:3000/users \
  -H "Content-Type: application/json" \
  -d '{"name": "Omar"}'

What each part does

express.json() lets Express read JSON sent in a POST request body. Without it, req.body will be empty.
app.get handles read requests. app.post handles create requests.
Status codes matter: 200 for success, 201 for created, 400 for a bad request, 404 for not found. They tell the client what happened without reading the message first.
Returning early, like return res.status(404)..., prevents the rest of the handler from running after an error.

Common beginner errors

Forgetting express.json(), then wondering why req.body is undefined.
Sending two responses in one handler, which causes a "headers already sent" error. Always return after sending an error response.
Using the same route twice with different logic. Express matches routes in order, so put specific routes before general ones when they overlap.
Storing data only in memory, as above. That is fine for learning, but data will disappear when the server restarts. A database comes next, once the API shape is clear.

Takeaway

You now have a working API pattern you can reuse: set up Express, add JSON handling, write GET and POST routes, use clear status codes, and validate input early. From here, the natural next steps are adding a database, validation, and authentication — each as its own small step, not all at once.

Originally published at https://practicaldevblog.blogspot.com/2026/10/build-your-first-rest-api-with-nodejs.html

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