A Beginner-Friendly Guide to Building Your First API Using Node.js

If you're new to backend development, building an API can feel intimidating.

But good news — with Node.js and Express, you can create a functional API in just a few minutes!

In this guide, you'll learn:

• What an API is
• How to set up a Node.js project
• How to build a simple REST API
• How to test it
• What to learn next

Let’s get started!

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What Is an API?

An API (Application Programming Interface) allows different applications to communicate with each other.

Example:

• Frontend: “Give me all users.”
• Backend API: “Here you go!”

Node.js + Express is one of the easiest ways to build APIs.

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Step 1: Initialize Your Project

mkdir my-first-api
cd my-first-api
npm init -y

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Step 2: Install Express

npm install express

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Step 3: Create Your First Server

Create server.js and add:

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

app.use(express.json());

// Home route
app.get('/', (req, res) => {
  res.send({ message: 'Welcome to your first Node.js API!' });
});

// Sample route
app.get('/api/users', (req, res) => {
  res.send([
    { id: 1, name: 'John' },
    { id: 2, name: 'Sarah' }
  ]);
});

// POST route
let users = [
  { id: 1, name: 'John' },
  { id: 2, name: 'Sarah' }
];

app.post('/api/users', (req, res) => {
  const newUser = {
    id: users.length + 1,
    name: req.body.name
  };

  users.push(newUser);
  res.status(201).send(newUser);
});

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

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Step 4: Run Your API

node server.js

You should see:

Server running on http://localhost:3000

Try opening:

• http://localhost:3000
• http://localhost:3000/api/users

Congrats — your first API is live!

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Step 5: Test the API

Using curl:

curl http://localhost:3000/api/users

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Bonus: Add a User With POST

Test with Postman:

{
  "name": "Emily"
}

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What to Learn Next

• Routing best practices
• Environment variables
• Connecting to MongoDB/PostgreSQL
• Authentication
• Deployment

You’re off to a great start — keep going! 🚀