Express App

Description 📋

A demo app for express

Installation 🔧

1. Clone this repo in git clone https://github.com/imranhsayed/express-app
2. git checkout branch-name

FAQs

1. What are Middlewares ? 🚦

• Middlewares are functions added to the stack, that have access to the request and response object.
• They are executed sequentially. We can do things like validation, authentication, data-parsing etc inside of each middleware.
• When the request comes in it passes through each of the middleware, before reaching the actual route.
• An express application is a stack of middleware running one after the other.
• The next() must be called at the end of every middleware ( function ), to move the processing to the next middleware in the stack.

2. Why do we use body-parser middleware?

• The body-parser middleware parses the form data, so that we can read it.
• Calling this function and setting extended to false, bodyParser.urlencoded( {extended: false} ) forces the use of node's native queryString module, which parses the data . It returns a middleware function that parses data.

const bodyParser = require( 'body-parser');
app.use( bodyParser.urlencoded( {extended: false} ) );

3. When is response.sendStatus() used?

• response.sendStatus( 200 ) is used in our express routes, when we don't want to send a body along with the response. It sets the response body to 'OK' by default.

4. How do we handle Multiple Route Instances?

• When we have multiple routes ( like get, post, delete ) for the same route url /posts , we can chain them together using app.route() like so:

 app.route( '/posts' )
    .get( ( req, res ) => ... )
    .post( ( req, res ) => ... )

• The app.route( $path ) takes the route path and returns a route object that handles all request to the given $path
• Chaining means calling the next function on the return value of the previous function.
• The lines starting with dot indicate the function calls on the object returned from the previous call.

6. How will you extract routes to modules?

• So that our main file does not become too long when we have many routes, we can extract routes by breaking them into modules.
• Create a dedicated folder for all your routes and create a separate file for each time of routes. E.g. dir name routes and filename will be posts.js inside of it, where we define all routes related to post
• Now in your routes/posts.js file, create an instance of a router using const router = express.Router(); and export router at the bottom
• Then we can define all our routes using the router instance like router.get(), or chain them using router.route()
• The path / is relative to where this router will be mounted in your main entry point file server.js

const express = require( 'express' );
const router = express.Router();

router.route( '/' )
   .all( (req, res) => ... )
   .get( (req, res) => ... )
   .post( (req, res) => ... );
   
router.get( '/:id', ( req, res ) => ... );    

module.exports = router;

• Notice that router.all() is used for all types of routes ( get, post, delete etc ) to that url.
• Finally we require this file routes/post.js into our main entry point file server.js

const posts = require( '/routes/posts' );
app.use( '/posts', posts );

• Another Example:

	// server.js
	const express = require( 'express' );
	const app = express();
	const port = 3000;
	
	const products = require( './routes/api/products' );
	
	app.use( '/api/products', products );
	
	app.listen( port => console.warn( `Ready on http://localhost:${port}` );
	
	
	
	// routes/api/products.js
	const express = require( 'express' );
	const router = express.Router();
	
	router.get( '/getProducts', ( req, res ) => ... );
	
	module.exports = router;

Branch Information 💻

1. static-middleware

The express.static() middleware that comes shipped with express, automatically servers the index.html on root url '/' without having to create a route using app.get( '/' )

app.use( express.static( 'public' ) )

2. custom-middleware

• Creates a custom middleware called loggerMiddleWare.
• Run npm run dev
• Open browser at http://localhost:5000
• Every time you refresh the page, a GET request to http://localhost:5000/ is made and the middleware intercepts that request and when the response for that request is finished it calculates the time it took for that request to complete and prints that.

• Also adds the message to a log.txt file

LoggerMiddleWare Demo 📹

3. query-params

• An example to create a route and get the post data at /posts
• If the user adds a query string ?limit=2 in the route, then it should return those many post items

Request with Query String Demo 📹

4. dynamic-routes

• An example to create a dynamic route at /posts/:name
• Request to /post/movies will return 'I love movie blogs'
• Request to /post/software will return 'I like Express'
• Request to name that's not available in post object, like /posts/xyz will return 'No description found for xyz'

const posts = {
	'movies': 'I love movie blogs',
	'games': 'The best game of the year is God of War 4',
	'software': 'I like Express'
};

// Dynamic Route
app.get( '/posts/:name', ( req, res ) => {

	const description = posts[ req.params.name ];

	// If the value of 'name' passed in the route does not exist as posts property
	if ( ! description ) {
		res.status( 404 ).json( `No description found for ${req.params.name}` );
	} else {
		res.json( description );
	}
} );

Dynamic Routes Demo 📹

Common Commands 💻

• npm run dev Starts Node server at http://localhost:5000