Nodejs express – MAlabdali

Express Overview

Express is a minimal and flexible Node.js web application framework that provides a robust set of features to develop web and mobile applications. It facilitates the rapid development of Node based Web applications. Following are some of the core features of Express framework −

Allows to set up middlewares to respond to HTTP Requests.
Defines a routing table which is used to perform different actions based on HTTP Method and URL.
Allows to dynamically render HTML Pages based on passing arguments to templates.

Installing Express

Firstly, install the Express framework globally using NPM so that it can be used to create a web application using node terminal.

$ npm install express --save

The above command saves the installation locally in the node_modules directory and creates a directory express inside node_modules. You should install the following important modules along with express −

body-parser − This is a node.js middleware for handling JSON, Raw, Text and URL encoded form data.
cookie-parser − Parse Cookie header and populate req.cookies with an object keyed by the cookie names.
multer − This is a node.js middleware for handling multipart/form-data.

$ npm install body-parser --save
$ npm install cookie-parser --save
$ npm install multer --save

Routing

var express = require('express');
var app = express();

app.get('/', function (req, res) {
   res.send('Hello World');
})

app.get(/a/, function (req, res) {//any url contains a
  res.send('/a/')
})

app.get('/name/:name',function (req,res){//req.params={name:"mohammed"}
    res.send("hello world");
});

var server = app.listen(8081, function () {
   var host = server.address().address;
   var port = server.address().port;
   
   console.log("Example app listening at http://%s:%s", host, port)
})

app.route('/book')
  .get(function (req, res) {
    res.send('Get a random book')
  })
  .post(function (req, res) {
    res.send('Add a book')
  })
  .put(function (req, res) {
    res.send('Update the book')
  })

static files

Express provides a built-in middleware express.static to serve static files, such as images, CSS, JavaScript, etc.
You simply need to pass the name of the directory where you keep your static assets, to the express.static middleware to start serving the files directly. For example, if you keep your images, CSS, and JavaScript files in a directory named public, you can do this −

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

upload file

var bodyParser = require('body-parser');
var multer  = require('multer');
let storage = multer.diskStorage({
    destination: (req, file, cb) => {
        cb(null,config.filesUploadPath);
    },
    filename: (req, file, cb) => {
        cb(null, file.originalname);
    },
});

let uploadFile = multer({
    storage: storage,
    limits: { fileSize: config.fileMaxSize }
}).single(config.fileQueryName);

const UploadFile = [uploadFile,async (req, res) => {
    try {
        let file=req[config.fileQueryName];
        fs.renameSync(file.destination+file.originalname,newName);
    } catch (err) {
    }
}];

cookies management

var express      = require('express')
var cookieParser = require('cookie-parser')

var app = express()
app.use(cookieParser())

app.get('/', function(req, res) {
   console.log("Cookies: ", req.cookies)
})
app.listen(8081)

middleware

app.get('/example/b', function (req, res, next) {
  console.log('the response will be sent by the next function ...')
  next()
}, function (req, res) {
  res.send('Hello from B!')
})

var cb0 = function (req, res, next) {
  console.log('CB0')
  next()
}

var cb1 = function (req, res, next) {
  console.log('CB1')
  next()
}

var cb2 = function (req, res) {
  res.send('Hello from C!')
}

app.get('/example/c', [cb0, cb1, cb2])//multiple response

let config=require("./config");
let express=require("express");

let app=express();
app.use(function(req,res,next){
    console.log("middleware");
    next();
});
app.get('/name',function (req,res){
    res.send(req.query);
});
let server=app.listen(config.port,()=>{
    console.log(server);
});

var express = require('express')
var router = express.Router()

// middleware that is specific to this router
router.use(function timeLog (req, res, next) {
  console.log('Time: ', Date.now())
  next()
})
// define the home page route
router.get('/', function (req, res) {
  res.send('Birds home page')
})
// define the about route
router.get('/about', function (req, res) {
  res.send('About birds')
})

module.exports = router

Content-Type: application/json

app.use(express.json())

Content-Type: application/x-www-form-urlencoded

app.use(express.urlencoded({
  extended: true
}))

and you can acess to it by

req.body.fieldName;

raw data

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

let options = {
    inflate: true,
    limit: '100kb',
    type: 'text/plain'
};
let app=express();
app.use(bodyParser.raw(options));

app.post("/hello",(req,res)=>{
    res.send(req.body);//body is string if type: 'text/*' else buffer
})
app.listen(8081,()=>{});

HTTP headers

app.get('/', (req, res) => {
  console.log(req.headers)
})

app.get('/', (req, res) => {
  req.header('User-Agent')
  req.get('User-Agent');
})

Response Methods And Properties

The methods on the response object (res) in the following table can send a response to the client, and terminate the request-response cycle. If none of these methods are called from a route handler, the client request will be left hanging.

Method	Description
res.download()	Prompt a file to be downloaded.
res.end()	End the response process.
res.json()	Send a JSON response.
res.jsonp()	Send a JSON response with JSONP support.
res.redirect()	Redirect a request.
res.render()	Render a view template.
res.send()	Send a response of various types.
res.sendFile()	Send a file as an octet stream.
res.sendStatus(), res.status(code)	Set the response status code and send its string representation as the response body.
res.app	hold express app
res.cookie() res.clearCookie()	res.cookie(name, value [, options])

res.set('Content-Type', 'text/html')

res.type('.html')
// => 'text/html'

res.type('html')
// => 'text/html'

res.type('json')
// => 'application/json'

res.type('application/json')
// => 'application/json'

res.type('png')
// => image/png:

for more visit this link

https://expressjs.com/en/4x/api.html