Express is a Node module, so in order to use it, we will need to import it into our program file. To create a server, the imported express function must be invoked.

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

On the first line, we import the Express library with require. When invoked on the second line, it returns an instance of an Express application. This application can then be used to start a server and specify server behavior.

The purpose of a server is to listen for requests, perform whatever action is required to satisfy the request, and then return a response. In order for our server to start responding, we have to tell the server where to listen for new requests by providing a port number argument to a method called app.listen(). The server will then listen on the specified port and respond to any requests that come into it.

The second argument is a callback function that will be called once the server is running and ready to receive responses.

const PORT = 4001; app.listen(PORT, () => { console.log(`Server is listening on port ${PORT}`); });

In this example, our app.listen() call will start a server listening on port 4001, and once the server is started it will log 'Server is listening on port 4001'.



Import express using require syntax and assign it to an express variable.

Create an instance of an Express server and save it to a variable named app.

Start the server listening on the port defined by the PORT variable. When the server has started, log a message to the console that the server is listening for requests.

To actually start your server listening, run the command node app.js to run your server in Node. At this point, it won’t do much, but if you’ve completed the steps above, it will log your message to show that the server started successfully.

When you want to check that you have written your starting server code correctly, use the ‘Check Work’ button.

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