Creating a New Express.js Application

Express.js is a popular Node.js web framework that allows developers to build robust and scalable web applications. In this section, we will walk through the process of creating a new Express.js application.

Prerequisites

To create a new Express.js application, you need to have Node.js installed on your machine. You can download the latest version of Node.js from the official Node.js website.

Step 1: Create a New Project Folder

Create a new folder for your project and navigate to it in your terminal or command prompt.

mkdir my-express-app
cd my-express-app

Step 2: Initialize a New Node.js Project

Initialize a new Node.js project by running the following command:

npm init -y

This command will create a new `package.json` file in your project folder.

Step 3: Install Express.js

Install Express.js by running the following command:

npm install express

Step 4: Create a New Express.js Application

Create a new file called `app.js` and add the following code:

const express = require('express');
const app = express();
const port = 3000;

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

app.listen(port, () => {
  console.log(`Server started on port ${port}`);
});

This code creates a new Express.js application and sets up a route for the root URL (`/`). When a GET request is made to the root URL, the application responds with the string "Hello World!".

Step 5: Start the Application

Start the application by running the following command:

node app.js

Open a web browser and navigate to `http://localhost:3000` to see the "Hello World!" message.

Conclusion

In this section, we created a new Express.js application from scratch. We initialized a new Node.js project, installed Express.js, and created a new Express.js application. We also set up a route for the root URL and started the application.

Frequently Asked Questions

Q: What is the purpose of the `package.json` file?

The `package.json` file is used to store metadata about your project, such as the project name, version, and dependencies.

Q: What is the difference between `npm install` and `npm install -g`?

`npm install` installs packages locally in your project folder, while `npm install -g` installs packages globally on your machine.

Q: How do I start the Express.js application?

You can start the Express.js application by running the command `node app.js` in your terminal or command prompt.

Q: What is the purpose of the `app.listen()` method?

The `app.listen()` method is used to start the Express.js application and listen for incoming requests on a specified port.

Q: How do I set up a new route in Express.js?

You can set up a new route in Express.js by using the `app.get()` method and specifying the route path and a callback function to handle the request.