ExpressJS Quick Start Guide

Express.js is a powerful and flexible web application framework for Node.js, which allows you to build APIs, web applications, and other types of services quickly and with ease. In this crash course, we will cover the basics of Express.js and show you how to create a simple web application using this framework.

1. Setting up your project:
   To get started with Express.js, you first need to install Node.js on your machine. You can download and install Node.js from the official website. Once you have Node.js installed, you can create a new directory for your project and navigate to it using the command line.

Next, you need to initialize a new Node.js project by running the following command:

npm init -y

This will create a package.json file in your project directory. Now, you can install Express.js by running the following command:

npm install express

1. Creating a simple Express application:
   Now that you have Express.js installed in your project, you can create a simple web application. Create a new file called app.js in your project directory and add the following code:

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

app.get('/', (req, res) => {
  res.send('Hello world!');
});

app.listen(3000, () => {
  console.log('Server running on port 3000');
});

In this code, we are creating a new Express application and defining a route for the root URL (/). When a request is made to this URL, the server will respond with the message "Hello world!". We are also starting the server and listening on port 3000.

1. Running your Express application:
   To run your Express application, you can simply run the following command in your project directory:

   node app.js

This will start the server and you should see the message "Server running on port 3000" in the console. Now, you can open your browser and navigate to http://localhost:3000 to see the message "Hello world!" displayed on the screen.

1. Adding more routes:
   Express allows you to define multiple routes and handle different types of requests. You can add more routes to your application by using the app.get() method for GET requests, app.post() for POST requests, app.put() for PUT requests, and app.delete() for DELETE requests.

Here is an example of adding a new route to your Express application:

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

Now, when you navigate to http://localhost:3000/about, you will see the message "About page" displayed on the screen.

1. Adding middleware:
   Middleware functions are functions that have access to the request object (req), the response object (res), and the next middleware function in the application’s request-response cycle. They can perform tasks such as authentication, logging, and error handling.

You can use middleware in Express by calling the app.use() method. Here is an example of adding a middleware function to log requests to the console:

app.use((req, res, next) => {
  console.log(`${req.method} ${req.url} ${new Date()}`);
  next();
});

Now, every time a request is made to your server, you will see the request method, URL, and timestamp logged to the console.

This crash course covers the basics of Express.js and shows you how to create a simple web application using this framework. Express.js is a powerful tool that can help you build robust and scalable applications quickly and efficiently. There is much more to learn about Express.js, including handling form data, working with databases, and using templates. I encourage you to explore the official documentation and experiment with different features to enhance your Express.js skills. Happy coding!