JavaScript Express App Listen

When it comes to building web applications with Node.js, Express is the most popular framework for creating scalable and robust applications. One essential aspect of any web application is setting up a server to listen to incoming requests from clients. In this guide, we'll explore how to use Express.js to create a server and start listening for incoming requests.

Creating an Express Server

The first step to creating an Express server is to install the framework using npm. Assuming you have Node.js and npm installed on your system, you can create a new project directory and initialize it with npm by running the following command in your terminal:

mkdir myproject && cd myproject
npm init -y

With the project initialized, you can install Express by running the following command:

npm install express

After installing Express, you can create a new file index.js in your project directory and import the module:

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

The express() function creates an instance of an Express application, which is a chain of middleware functions. Middleware functions are functions that have access to the request and response objects, and they can modify those objects or perform additional tasks.

Setting Up a Basic Route

To listen to incoming requests, we need to define a route that can handle the request and send a response back to the client. In Express, routes are URL paths that are associated with a callback function, which is executed when a request is made to the path.

Let's define a basic route that sends the text "Hello, World!" back to the client when a request is made to the root path /:

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

The app.get() function associates a route with an HTTP GET request method. When a GET request is made to the path /, the function passed as the second argument is executed. In this case, the function sends the text "Hello, World!" back to the client.

Listening for Incoming Requests

To start listening for incoming requests, we need to bind to a port on our server. We can pass a port number and a callback function to the app.listen() function to start listening:

const port = 3000;

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

The app.listen() function starts an HTTP server that listens on the specified port. When a request is made to the server, the server invokes the appropriate route handler function, and sends a response back to the client.

Conclusion

In this guide, we explored how to create an Express server and listen for incoming requests. We defined a basic route handler function, and used the app.listen() method to start the server. With this knowledge, you should be able to build simple Express servers that can handle incoming requests from clients.