Express.js Setup and Server Creation

Setting up Express.js

• Node.js is required for Express.js.
• npm init -y creates a package.json file for dependency management.
• Install Express.js using npm i express. Versions 4 and 5 are supported.
• Install Nodemon as a development dependency: npm i --save-dev nodemon.
• Create a dev start script in package.json to run nodemon server.js. This restarts the server when code changes.

Creating a Server

• Create a server.js file for server logic.
• Import Express: const express = require('express');
• Initialize the Express app: const app = express();
• Start the server: app.listen(3000);

Setting up Routes

• app.get(path, function(req, res)) defines a GET route.
• path specifies the URL (e.g., /).
• req is the incoming request, res is the response.
• Send a message with res.send("message").
• res.sendStatus(statusCode) sends a status code (e.g., 500 for errors)

Express.js Response

• res.status(code).send(message) sends a status code and message.
• res.json(data) sends JSON data.
• res.download(filePath) sends a file for download.
• res.render(viewPath) renders an HTML file.

Creating Views

• Express looks for views in the views folder.
• ejs are used to generate HTML content.
• Install ejs: npm install ejs.
• Configure ejs: app.set('view engine', 'ejs').
• .ejs files are used instead of .html.
• Use <% %> for server-side code, and <%= %> for output.

Passing Data to Views

• res.render(viewPath, { data: 'value' }) passes data to the view.
• Access data in the view using locals: <%= locals.data %>.

Express Routers

• Import Express: const express = require('express');
• Create a router: const router = express.Router();
• router.get(), router.post(), etc. define routes inside the router.
• app.use('/path', router) mounts the router to a path.

Dynamic Routes

• router.get('/users/:id', ...) defines a route with dynamic parameter id.
• Access the parameter as req.params.id.

Clean Route Structure

• Separate routes into files (e.g., users.js) for better organization.
• Import these files into your main server file and use router instances.

Request Method Example: POST

• router.post('/users', ...) handles POST requests to the /users route.
• POST is used for creating resources.

Dynamic Parameters and Route Ordering

• Routes are processed sequentially (top-to-bottom).
• Dynamic routes (/user/:id) match any value after the placeholder.
• Static routes (/new) should be placed above dynamic routes.

Route Chaining with router.route

• router.route method chains methods (GET, PUT, DELETE) for a single path.
• This improves route handling efficiency.

Middleware and router.param

• Middleware runs between request and response.
• router.param creates middleware for parameters.

Example of Middleware: Logging

• Middleware can log request details.
• app.use applies middleware to all routes.
• Router-specific middleware applies only to associated routes.

Built-in Middleware

• express.static serves static files.
• express.urlencoded parses URL-encoded data from forms.
• express.json parses JSON data from requests.

Example of Form Handling

• Forms submit to /users route.
• request.body contains form data (requires express.urlencoded).

Query Parameters

• Access query parameters via request.query: e.g., request.query.name.