Introduction to Express

In this class, we covered fundamental concepts related to the HTTP protocol, status codes, and an introduction to the Express framework.

HTTP Protocol Basics

HTTP (Hypertext Transfer Protocol) is the foundation of data communication on the World Wide Web. It is a protocol for transmitting hypermedia documents, such as HTML. In the context of web development, there are two primary types of HTTP requests:

• GET Request: Used to request data from a specified resource. For example, when you visit a webpage, your browser sends a GET request to the server to retrieve the HTML, CSS, and other assets needed to render the page.

• POST Request: Used to submit data to be processed to a specified resource. When you submit a form on a web page, the data is often sent to the server using a POST request.

Status Codes

Here are some commonly encountered status codes:

• 200 OK: The request was successful, and the server responded with the requested data.

• 404 Not Found: The server could not find the requested resource. This often occurs when a URL is mistyped or the resource has been removed.

• 500 Internal Server Error: A generic error message returned when an unexpected condition was encountered on the server. This indicates that there is an issue on the server side.

Express Framework

Express is a minimal and flexible Node.js web application framework that provides a robust set of features to develop web and mobile applications. It simplifies the process of building web servers and handling HTTP requests.

Key features of Express include:

• Routing: Express allows you to define routes that map to specific URL patterns. In the provided code, we have routes for the root path ("/"), "/about", and handling both GET and POST requests.

• Middleware: Middleware functions are functions that have access to the request object (req), the response object (res), and the next function in the application’s request-response cycle. The body-parser middleware, used in the code, is responsible for parsing incoming JSON requests.

Code Example

const express = require("express");
const bodyParser = require("body-parser");

const app = express();
const port = process.env.PORT || 3005;

app.use(bodyParser.json());

// Handling GET requests
app.get('/', (req, res) => {
    res.send('Hello World!');
});

app.get('/about', (req, res) => {
    res.send('About us');
});

// Handling POST requests
app.post('/', (req, res) => {
    console.log(req.body);
    res.send('Hello World!');
});

// Server Listening
app.listen(port, () => {
    console.log(`Example app is listening at port ${port}`);
});