expressjsHow do I use the Express.js library to create a web application?

Express.js is a web application framework for Node.js that provides a robust set of features for web and mobile applications. It is used to build web applications and APIs.

To use Express.js to create a web application, you will need to install the Express.js library. This can be done using the Node Package Manager (npm).

Once installed, you can create your web application by writing the code in JavaScript. Here is an example of a basic Express.js web application:

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

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

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

This code creates a web server that will listen on port 3000 and respond with "Hello World!" when a user visits the root path.

The code is composed of the following parts:

• const express = require('express');: This imports the Express.js library.
• const app = express();: This creates a new Express application.
• app.get('/', (req, res) => {...});: This defines a route handler for the root path, which will be called when a user visits the root path.
• const port = process.env.PORT || 3000;: This sets the port that the web server will listen on.
• app.listen(port, () => {...});: This starts the web server and tells it to listen on the port specified.

Output example

Listening on port 3000...

For more information on Express.js, check out the Express.js documentation.

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