Example 1: express hello world
//to run : node filename.js
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}`))
//visit localhost:3000
// assuming you have done 1) npm init 2) npm install express
Example 2: app.get
const express = require('express');
const app = express();
const { getElementById, getIndexById, updateElement,
seedElements, createElement } = require('./utils');
const PORT = process.env.PORT || 4001;
// Use static server to serve the Express Yourself Website
app.use(express.static('public'));
const expressions = [];
seedElements(expressions, 'expressions');
const animals = [];
seedElements(animals, 'animals');
// Get all expressions
app.get('/expressions', (req, res, next) => {
res.send(expressions);
});
// Get a single expression
app.get('/expressions/:id', (req, res, next) => {
const foundExpression = getElementById(req.params.id, expressions);
if (foundExpression) {
res.send(foundExpression);
} else {
res.status(404).send();
}
});
// Update an expression
app.put('/expressions/:id', (req, res, next) => {
const expressionIndex = getIndexById(req.params.id, expressions);
if (expressionIndex !== -1) {
updateElement(req.params.id, req.query, expressions);
res.send(expressions[expressionIndex]);
} else {
res.status(404).send();
}
});
// Create an expression
app.post('/expressions', (req, res, next) => {
const receivedExpression = createElement('expressions', req.query);
if (receivedExpression) {
expressions.push(receivedExpression);
res.status(201).send(receivedExpression);
} else {
res.status(400).send();
}
});
// Delete an expression
app.delete('/expressions/:id', (req, res, next) => {
const expressionIndex = getIndexById(req.params.id, expressions);
if (expressionIndex !== -1) {
expressions.splice(expressionIndex, 1);
res.status(204).send();
} else {
res.status(404).send();
}
});
// Get all animals
app.get('/animals', (req, res, next) => {
res.send(animals);
});
// Get a single animal
app.get('/animals/:id', (req, res, next) => {
const animal = getElementById(req.params.id, animals);
if (animal) {
res.send(animal);
} else {
res.status(404).send();
}
});
// Create an animal
app.post('/animals', (req, res, next) => {
const receivedAnimal = createElement('animals', req.query);
if (receivedAnimal) {
animals.push(receivedAnimal);
res.status(201).send(receivedAnimal);
} else {
res.status(400).send();
}
});
// Update an animal
app.put('/animals/:id', (req, res, next) => {
const animalIndex = getIndexById(req.params.id, animals);
if (animalIndex !== -1) {
updateElement(req.params.id, req.query, animals);
res.send(animals[animalIndex]);
} else {
res.status(404).send();
}
});
// Delete a single animal
app.delete('/animals/:id', (req, res, next) => {
const animalIndex = getIndexById(req.params.id, animals);
if (animalIndex !== -1) {
animals.splice(animalIndex, 1);
res.status(204).send();
} else {
res.status(404).send();
}
});
app.listen(PORT, () => {
console.log(`Server is listening on ${PORT}`);
});
Example 3: what is app.use() used for
//app.get will see only exact match ex.> "/book" here app.get will not allow /book/1, etc
//but app.use is different see below
//what is difference between app.use and app.all
//app.use takes only 1 callback while app.all takes multiple callbacks
//app.use will only see whether url starts with specified path But, app.all() will match the complete path
app.use( "/book" , middleware);
// will match /book
// will match /book/author
// will match /book/subject
app.all( "/book" , handler);
// will match /book
// won't match /book/author
// won't match /book/subject
app.all( "/book/*" , handler);
// won't match /book
// will match /book/author
// will match /book/subject
Example 4: express router middleware
var express = require('express')
var app = express()
var router = express.Router()
// a middleware function with no mount path. This code is executed for every request to the router
router.use(function (req, res, next) {
console.log('Time:', Date.now())
next()
})
// a middleware sub-stack shows request info for any type of HTTP request to the /user/:id path
router.use('/user/:id', function (req, res, next) {
console.log('Request URL:', req.originalUrl)
next()
}, function (req, res, next) {
console.log('Request Type:', req.method)
next()
})
// a middleware sub-stack that handles GET requests to the /user/:id path
router.get('/user/:id', function (req, res, next) {
// if the user ID is 0, skip to the next router
if (req.params.id === '0') next('route')
// otherwise pass control to the next middleware function in this stack
else next()
}, function (req, res, next) {
// render a regular page
res.render('regular')
})
// handler for the /user/:id path, which renders a special page
router.get('/user/:id', function (req, res, next) {
console.log(req.params.id)
res.render('special')
})
// mount the router on the app
app.use('/', router)