Express Framework Tutorial

1. Introduction

Goal

This tutorial aims to introduce you to the Express framework, a flexible, minimalist web application framework for Node.js. You'll learn how to set up an Express application and create a simple server.

Learning Outcomes

By the end of this tutorial, you'll be able to:
- Install Express via npm
- Create a basic Express app
- Understand the fundamental concepts of Express, such as routing and middleware

Prerequisites

• Basic understanding of Node.js
• Node.js and npm installed on your local development machine

2. Step-by-Step Guide

Installation

Express can be installed via npm (Node Package Manager). To add it to your project, navigate to your project directory in your terminal and type:

npm install express --save

Creating an Express application

To start, create a new file, app.js, in your project's root directory. Here's a simple Express application:

const express = require('express');
const app = express();
const port = 3000;

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

app.listen(port, () => {
  console.log(`Example app listening at http://localhost:${port}`)
});

Explaining the code

• const express = require('express'); - This imports the Express module.
• const app = express(); - This creates an instance of an Express application.
• app.get('/', (req, res) => {...}); - This is a route definition. When a GET request is made to the root of the app, the callback function is called.
• app.listen(port, ()=>{...}); - This makes the app listen for requests on the specified port.

3. Code Examples

Code Example 1: Basic Routing

Express uses routes to determine how an application responds to client requests. Here's an example:

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

• app.get is the method, corresponding to HTTP's GET.
• '/about' is the path on the server.
• (req, res) => {...} is the handler function, executed when the route is matched.

The expected output when you navigate to 'http://localhost:3000/about' would be the text 'About Page'.

Code Example 2: Using Middleware

Middleware are functions that process incoming requests. Here's an example of a middleware function:

app.use((req, res, next) => {
  console.log('Time:', Date.now());
  next();
});

• app.use is a method to use a middleware function.
• (req, res, next) => {...} is the middleware function. It logs the current time and passes control to the next middleware function.

4. Summary

In this tutorial, you've learned how to:
- Install Express
- Create a basic Express app
- Understand routing and middleware in Express

Next Steps

To further your understanding of Express, try building a simple application that uses different HTTP methods and multiple routes.

Additional Resources

• Express.js Official Documentation
• Node.js Documentation

5. Practice Exercises

Exercise 1: Hello, Express!

Create an Express server that responds with "Hello, Express!" when a GET request is made to the homepage.

Solution

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

Exercise 2: Middleware Logger

Create a middleware that logs the details of every request (method, path, and time).

Solution

app.use((req, res, next) => {
  console.log(`Method: ${req.method}, Path: ${req.path}, Time: ${Date.now()}`);
  next();
});

These exercises will help you get a feel for building with Express. Keep experimenting with different types of requests, routes, and middleware.