Working with Express.js

 

Whats in the module :

 


 

 

 

What is Express.js : 




Installing Express.js: To install the expressjs into your app , you have to run - npm install --save express


Adding Middleware: 


example : 

    

const http =require('http');

const express = require('express');

const app = express();

app.use((req , res , next)=>{
console.log('In the middleware!');
next();//Allow the request  to continue to the next middleware in line
});

app.use((req , res, next)=>{
console.log('In another middleware!');
})

const server = http.createServer(app)//app is act As a valid request handler.

//listening to a port for request
server.listen(3000);
console.log('listening to port 3000');
 
 
Handling Different Routes :  
    
               
const express = require('express');

const app = express();

// app.use((req, res, next) => {
// console.log('First Middleware');
// next();
// });

// app.use((req, res, next) => {
// console.log('Second Middleware');
// res.send('<p>Assignment solved (almost!)</p>');
// });

app.use('/users', (req, res, next) => {
console.log('/users middleware');
res.send('<p>The Middleware that handles just /users</p>');
});

app.use('/', (req, res, next) => {
console.log('/ middleware');
res.send('<p>The Middleware that handles just /</p>');
});


app.listen(3000);
 
 
Parsing Incoming Requests: To parse the request body we can use the body-parser npm package that will gives us the object like data of requested body of data.
Example : 
     
        
const express = require('express');
const bodyParser = require('body-parser');

const app = express();
app.use(bodyParser.urlencoded({extended:false}));

app.use('/add-product',(req, res, next) => {
// console.log('In the add-product middleware!');
res.send('<form action="/product" method="POST"><input type="text" name="title"><button type="submit">add product</button></form>')

});

app.use('/product',(req , res , next)=>{
console.log(req.body);
res.redirect('/');
})

app.use('/',(req, res, next) => {
// console.log('In another middleware!');
res.send('<h1>Hello message from express js </h1>');
})
//listening to the port
app.listen(3001);

// const server = http.createServer(app)

// //listening to a port for request
// server.listen(3000);
console.log('listening to port 3001');


 
 Limiting Middleware Execution to POST Requests : 
     Now the above /product middleware will work for both post as well as get request . To limit the /product middle ware for only post request we have to use the express http verbs like : get , post , put , patch or delete.Although these verbs also check the url for exact match.

example : 
    
               
const express = require('express');
const bodyParser = require('body-parser');

const app = express();
app.use(bodyParser.urlencoded({extended:false}));

app.use('/add-product',(req, res, next) => {
// console.log('In the add-product middleware!');
res.send('<form action="/product" method="POST"><input type="text" name="title"><button type="submit">add product</button></form>')

});

app.post('/product',(req , res , next)=>{
console.log(req.body);
res.redirect('/');
})

app.use('/',(req, res, next) => {
// console.log('In another middleware!');
res.send('<h1>Hello message from express js </h1>');
})
//listening to the port
app.listen(3001);

// const server = http.createServer(app)

// //listening to a port for request
// server.listen(3000);
console.log('listening to port 3001');




Using Express Router :

admin.js : 


const express = require('express');

const router = express.Router();

router.get('/add-product',(req, res, next) => {
// console.log('In the add-product middleware!');
res.send('<form action="/product" method="POST"><input type="text" name="title"><button type="submit">add product</button></form>')

});

router.post('/product',(req , res , next)=>{
console.log(req.body);
res.redirect('/');
})



module.exports = router;

shop.js :
    
   
const express = require('express');

const router = express.Router();

router.get('/',(req, res, next) => {
// console.log('In another middleware!');
res.send('<h1>Hello message from express js </h1>');
})
module.exports = router;
 
app.js :
 
    
const express = require('express');
const bodyParser = require('body-parser');
const adminRoutes = require('./routes/admin');
const userRoutes = require('./routes/shop');
const app = express();
app.use(bodyParser.urlencoded({extended:false}));

app.use(adminRoutes);

app.use(userRoutes);

//listening to the port
app.listen(3001);

// const server = http.createServer(app)

// //listening to a port for request
// server.listen(3000);
console.log('listening to port 3001');


 
 
Adding a 404 Error Page: Add these line at the bottom of all the routes.
 
app.use((req , res , next)=>{
res.status(404).send('<h1>Page not found!</h1>');
})
 
 Filtering Paths:
  If our routes has some starting point let say /admin/routes then we can configure our routes to reach that routes from app.js file. ANd we can use the same routes for different requests methods.

admin.js :
           
// /admin/add-product => GET
router.get('/add-product',(req, res, next) => {
// console.log('In the add-product middleware!');
res.send('<form action="/admin/add-product" method="POST"><input type="text" name="title"><button type="submit">add product</button></form>')

});
// /admin/add-product => POST
router.post('/add-product',(req , res , next)=>{
console.log(req.body);
res.redirect('/');
})

app.js :
         
app.use('/admin',adminRoutes);


Using a Helper Function for Navigation: 

rootPath.js :


const path = require('path');
module.exports = path.dirname(process.mainModule.filename);

admin.js :

const rootDir = require('../util/rootpath');
const router = express.Router();

router.get('/add-product',(req, res, next) => {
// console.log('In the add-product middleware!');
res.sendFile(path.join(rootDir,'views','add-product.html'));

});

shop.js :


const path = require('path');
const express = require('express');
const rootDir = require('../util/rootpath');
const router = express.Router();

router.get('/',(req, res, next) => {
// console.log('In another middleware!');
// res.send('<h1>Hello message from express js </h1>');
res.sendFile(path.join(rootDir,'views','shop.html'));
})
module.exports = router;



Module summary : 
 

 





 
 
 

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