Web 322 - Express Basics

Web 322 - Express Basics

• This lecture covers Express, a popular and flexible Node.js framework for building web applications and APIs.

Node.js Review

• Node.js is a JavaScript runtime environment.
• Node.js allows building web applications and APIs.
• Alternatives to Node.js exist.
• Advantages of Node.js are discussed in the slides.

Modules vs Libraries

• Modules are libraries in Node.js; a set of functions for inclusion in an application.
• Examples of modules include Circle.js, Rectangle.js, and Square.js.
• Packages group modules or libraries together.
• Node.js uses a package manager to find and install packages (like NPM).

Modules in Node.js

• Modules organize functionality into files (simple or complex).
• Modules are reusable throughout applications.
• Each module has its own context and doesn't interfere with other modules, preventing scope pollution.
• Core modules load automatically when Node.js starts.
• Third-party modules need installation (like NPM).
• Local modules are created by developers for specific application functionalities.

Core Node.js Modules

• The http and https modules create HTTP servers.
• The fs module handles file input/output (I/O).
• The path module manages file paths.
• The os module provides information about the operating system.

What is NPM?

• NPM (Node Package Manager) is the official package manager for Node.js.
• It's a command-line client and an NPM registry (online database of packages).
• NPM is bundled and installed automatically with Node.js.

NPM & Packages

• Packages are managed through NPM.
• The diagram shows how local projects, core packages, and dependencies are managed via NPM.

Basic NPM Commands

• npm init or npm init -y creates a package.json file (project manifest).
• npm install <package name> or npm i <package name> installs a 3rd-party package locally.
• npm remove <package name> removes a package.

Node Commands

• Execute JavaScript programs with node <entry-point filename>.
• The .js extension can be omitted.

Package.json File

• package.json is central to the Node.js ecosystem, like a manifest.
• It manages applications, modules, packages, and other metadata.

What is Express?

• Express is a popular and flexible Node.js framework.
• It's designed for building web applications and APIs.
• It's a standard server framework for Node.js.
• Express simplifies handling requests and routes.

Alternative Frameworks to Express

• Vanilla Node.js, Adonis.js, Koa, and Sails.js are alternatives to Express.

Frameworks vs Libraries

• Both frameworks and libraries contain code written by others, often used to address common problems.
• Libraries allow you to control the application flow, choosing when and where to call functions.
• Frameworks dictate the application flow, providing places to plug in custom code.

Middleware

• Middleware functions in Express handle requests until a response is sent to the browser.
• Express middleware functions have access to the request and response objects.

What Can We Do With Express?

• Express handles HTTP requests.
• It supports handling responses on specific URLs.
• It supports various templating engines.

Routing

• Routing in Express handles URLs mapped to client access.
• A route is a path on a website handling requests.

Three Core Objects of Express (app)

• The app object in Express provides functionalities like attaching local variables (locals), starting the listening process (listen()) and adding middlewares (use()).

Three Core Objects of Express (req)

• The req object (request) contains information like the request body and cookies.
• It includes dynamically read values from URLs, query strings and headers.

Three Core Objects of Express (res)

• The res object (response) manages server responses to requests.
• It enables setting cookies, handling file downloads, ending responses, sending JSON objects and redirects.

Serving Static Files

• Static files (like CSS & images) aren't dynamic.
• Use the app.use(express.static("static")); method. Static resources can load from folders without needing to add them into the URL.

Error Handling

• Middleware facilitates error handling.
• Code includes error parameters like handleClientError(err, req, res, next).
• next() transfers control to the next error handler; errors can be logged.

Processing Form Data

• body-parser processes (text-based e.g. forms) submissions.
• multer or express-fileupload handles multi-part submissions (text & files).

Demo of Express

• A demo illustrating Express usage is available.