why express project package.json does not have http module dependency

In an Express project, you typically won't see the http module listed as a dependency in the package.json file. This is because the http module is a core module of Node.js and does not need to be explicitly installed or listed as a dependency. Express leverages this core module internally to create HTTP servers.

Here's a detailed explanation of how Express uses the http module under the hood:

How Express Uses the http Module

1. Express Application Initialization: When you create an Express application, you are essentially creating an instance of the Express application, which is a function that can be called by an HTTP server.

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

2. app.listen Method: The app.listen method is a convenience method in Express that simplifies the creation of an HTTP server. Internally, it uses the http.createServer method from the Node.js core http module to create the server.

   Here's an example of using the app.listen method:

   const express = require('express');
   const app = express();
   
   app.get('/', (req, res) => {
     res.send('Hello, World!');
   });
   
   app.listen(3000, () => {
     console.log('Server is running on port 3000');
   });
   

3. Internal Implementation of app.listen: To understand how Express uses the http module, let's look at the internal implementation of the app.listen method. This method is defined in the application.js file within the Express source code.

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

   In this implementation:

   • require('http') imports the core http module.
   • http.createServer(this) creates an HTTP server, with this referring to the Express application. The Express application is a function that can handle HTTP requests.
   • server.listen.apply(server, arguments) calls the listen method on the created server, passing any arguments provided to app.listen.

4. Handling Requests: The Express application function is passed to http.createServer. This function acts as the request listener for the server. When an HTTP request is received, the server calls this function, which processes the request using Express's middleware and routing system.

5. Middleware and Routing: Express enhances the basic HTTP server functionality by adding middleware and routing capabilities. Middleware functions in Express can modify the request and response objects, end the request-response cycle, and pass control to the next middleware function in the stack.

   app.use((req, res, next) => {
     console.log('Middleware 1');
     next();
   });
   
   app.get('/', (req, res) => {
     res.send('Hello, World!');
   });
   
   app.listen(3000);
   

Why You Don’t See http in package.json

• Core Module: The http module is a built-in core module of Node.js. Core modules do not need to be installed via npm and do not need to be listed as dependencies in package.json.
• Express Abstraction: Express abstracts away the low-level details of creating and managing the HTTP server, providing a higher-level API for building web applications. This abstraction simplifies application development and hides the underlying complexity.
• No Explicit Dependency: Since the http module is always available in the Node.js runtime, there is no need to explicitly declare it as a dependency in package.json.

Example Project Structure

Here’s an example of what a typical Express project’s package.json might look like:

{
  "name": "express-app",
  "version": "1.0.0",
  "description": "A simple Express application",
  "main": "index.js",
  "scripts": {
    "start": "node index.js"
  },
  "dependencies": {
    "express": "^4.17.1"
  }
}