At what point is the JavaScript function expression triggered in this code snippet?

Question

At what point is the JavaScript function expression triggered in this code snippet?

let express = require('express')

let app = express();

app.use(express.static('static'));

let server = app.listen(3000, function() {
    let port = server.address().port;
    console.log("The server has started on port", port);
});

I am new to JavaScript. In this code snippet, the server() function is never explicitly called, yet it still executes. It is not an immediately invoked function expression (IIFE). I'm curious about when exactly the app.listen() method gets executed.

Original code sourced from: https://github.com/vasansr/react-tutorial-mern/blob/master/webapp.js

javascript node.js express

Answer 1

Answer №1

As soon as the line is reached, app.listen gets executed.

The server now listens on port 3000: var server = app.listen(3000, function() { ...

Port 3000 is now open for incoming connections.

The callback function in the second parameter of listen will trigger when a connection is made to port 3000.

Answer 2

As soon as the line is reached, app.listen gets executed.

The server now listens on port 3000: var server = app.listen(3000, function() { ...

Port 3000 is now open for incoming connections.

The callback function in the second parameter of listen will trigger when a connection is made to port 3000.

Answer 3

Answer №2

According to the information found in the documentation of expressjs:

The method app.listen() is designed to return an http.Server object and serves as a shortcut for the following code:

app.listen = function() {
  var server = http.createServer(this);
  return server.listen.apply(server, arguments);
};

Answer 4

According to the information found in the documentation of expressjs:

The method app.listen() is designed to return an http.Server object and serves as a shortcut for the following code:

app.listen = function() {
  var server = http.createServer(this);
  return server.listen.apply(server, arguments);
};

Answer 5

Answer №3

The server isn't a function, it's actually a variable. The code snippet app.listen(...) is being run directly on line 7. The outcome of this action is then stored in the variable server.

The app.listen() function contains a callback method as its second parameter. This callback gets triggered once the app begins listening for requests. At that point, calling server.address().port will provide you with the server's port number.

Answer 6

The server isn't a function, it's actually a variable. The code snippet app.listen(...) is being run directly on line 7. The outcome of this action is then stored in the variable server.

The app.listen() function contains a callback method as its second parameter. This callback gets triggered once the app begins listening for requests. At that point, calling server.address().port will provide you with the server's port number.

Answer 7

Answer №4

It appears that the server is not being utilized in any part of the code. It's worth noting that the server may be an object returned from the app.listen function rather than a traditional function.

Answer 8

It appears that the server is not being utilized in any part of the code. It's worth noting that the server may be an object returned from the app.listen function rather than a traditional function.

At what point is the JavaScript function expression triggered in this code snippet?

Answer №1

Answer №2

Answer №3

Answer №4

Similar questions

How can I properly integrate multer with Node and Express in this situation?

Persistently save retrieved information and store data in MongoDB by utilizing Node.js

Tips for displaying previous values when discarding changes to a record in a material-ui table

Instead of scrolling through the entire window, focus on scrolling within a specific HTML element

Utilizing the mobile navigation layout for desktop screens without the need to adjust breakpoints

Direct the /username path to /[user]/[tab].js instead of [user]/index.js in Next.js

Splitting the div into two columns

The background image refuses to load

Techniques for retrieving user inputs upon loading the HTML document and detecting changes using JavaScript

Testing the screen size automatically using Javascript

Utilizing Gitlab Runner to store node_modules as an artifact rather than in the cache

Is the input in the array? How to find out?

Executing a Shortcode Using a Button in Visual Composer for Wordpress

Steps to generate a fresh array from a given array of objects in JavaScript

The package "XXX" could not be located within the "npm" registry

Effortless creation of REST APIs for performing CRUD operations on MongoDB

Changing a file object into an image object in AngularJS

React's conditional statement is malfunctioning

Creating curved triangles in React Native is a fun and easy way to add stylish

The lambda function is encountering a MySQL error stating that it cannot find the module 'mysql' and is not functioning properly, even after being included in the zipped file