How to Create an Express App: Simple Steps to Start

To create an Express app, first install Express with npm install express. Then, create a JavaScript file where you import Express, create an app instance with express(), define routes, and start the server with app.listen().

Syntax

The basic syntax to create an Express app includes importing Express, creating an app instance, defining routes, and starting the server.

• const express = require('express'): Imports the Express library.
• const app = express(): Creates an Express app instance.
• app.get(path, handler): Defines a route for GET requests.
• app.listen(port, callback): Starts the server on the specified port.

javascript

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

app.get('/', (req, res) => {
  res.send('Hello World!');
});

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

Example

This example shows a complete Express app that responds with "Hello World!" when you visit the home page. It listens on port 3000 and logs a message when the server starts.

javascript

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

app.get('/', (req, res) => {
  res.send('Hello World!');
});

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

Output

Server running on http://localhost:3000

Common Pitfalls

Common mistakes when creating an Express app include:

• Not installing Express before running the app (npm install express is required).
• Forgetting to call app.listen() to start the server.
• Using incorrect route paths or HTTP methods.
• Not handling asynchronous code properly in route handlers.

javascript

/* Wrong: Missing app.listen() - server won't start */
const express = require('express');
const app = express();
app.get('/', (req, res) => {
  res.send('Hello');
});

/* Right: Include app.listen() */
app.listen(3000, () => {
  console.log('Server started');
});

Quick Reference

Remember these key steps to create an Express app:

• Install Express with npm install express.
• Import Express and create an app instance.
• Define routes with app.get(), app.post(), etc.
• Start the server with app.listen(port).

Key Takeaways

Install Express using npm before creating your app.

Create an app instance with express() to start defining routes.

Always call app.listen() to start the server and listen on a port.

Define routes to handle different HTTP requests and send responses.

Check for common mistakes like missing app.listen() or wrong route paths.