Express app.listen() Function
app.listen() in Express is like telling your app to start listening for visitors on a specific address and port, much like how Node listens for connections. The app, created by `express()`, is just a handy function that handles different types of requests, making it easy to serve both HTTP and HTTPS versions of your app without extra complexity.
Syntax:Â
app.listen([port[, host[, backlog]]][, callback])
Parameters:
- Port: It specifies the port on which we want our app to listen.
- Â Host (Optional): It specifies the IP Address of the host on which we want our app to listen. You can specify the host if and only if you have already specified the port. ( since you have a closing(‘]’) bracket after ([, host[, backlog]]) as you can see in the above syntax, so this means the port must be specified before specifying host and backlog).
- Backlog (Optional): It specifies the max length of the queue of pending connections. You can specify the backlog if and only if you have already specified the port and host. ( since you have a closing bracket after ([, backlog]), so this means you will have to specify the host before specifying backlogs)
- Callback (Optional): Â It specifies a function that will get executed, once your app starts listening to the specified port. You can specify callback alone i.e., without specifying port, host, and backlogs.( since this is a separate set of arguments in opening and closing brackets([, callback]), this means you can specify these arguments without specifying the argument of previous opening and closing square brackets.
Steps to Install the express module:
Step 1: You can install this package by using this command.
npm install express
Step 2: After installing the express module, you can check your express version in the command prompt using the command.
npm version express
Project Structure:
Project Structure
The updated dependencies in package.json file will look like:
"dependencies": {
"express": "^4.18.2",
}
Example 1: Below is the code of app.listen() Function implementation.
Javascript
const express = require( 'express' );
const app = express();
const PORT = 3000;
app.listen(PORT, function (err){
if (err) console.log( "Error in server setup" )
console.log( "Server listening on Port" , PORT);
})
|
Steps to run the program:Â
Run the index.js file using the below command:Â
node index.js
Output:Â Â
Server listening on Port 3000
So this is how you can use the Express app.listen() function which Binds and listens for connections on the specified host and port.
Last Updated :
01 Jan, 2024
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