Express JS Node JS web framework

Install Express

npm install express

Create Express Server

const express=require('express');
const app= express();
const PORT=2000;
app.listen(PORT, ()=>{
console.log('Server running...')
})

Create route

app.get("/", (req, res)=>{
   res.send('Welcome to home page');
})

Request Object

• .hostname() - Return hostname.
• .ip() - Return IP address.
• .method() - Return request method,
• .originalUrl() - Return request URL.
• .params() - Return route parameters.
• .path() - Return path.
• .query() - Return query string variables.
• .route() - Return route configuration.
• .secure() - Check connection is secure or not.
• .xhr() - Check request is xhr or not.

Response Object

• .send() - Sends http response.
• .status() - Set http status.
• .render() - Render a view and send rendered HTML string to the client.
• .redirect() - Redirect one location to another.
• .json() - Send JSON format data.
• .download(file_name, new_name, (err)) - Download files.

Set logger in app

Package: morgan

Install: npm install morgan

Load

const logger= require('morgan')

Use Logger

app.use(logger('dev'))

Fetch static files

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

Set up view engine

Template: EJS (Embedded Java Script)

Install

npm install ejs

app.set('views', path.join(__dirname, "views"))
app.set("view engine", "ejs")

Parse form submitted data

Package: body-parser

Install

npm install body-parser

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

Template Engine (EJS)

Node JS & MYSQL

Install

npm install mysql

Load MySQL

let mysql=require('mysql')

Establish connection of NODE JS with MYSQL

let config={
     host:'localhost',
     user:'username',
     password:'password',
     database:'database_name'
};

let conn= mysql.createConnection(config);
conn.connect( (error)=>{
    if(error) throw error;
    let sql="sql query";
    conn.query(sql, (error, result)=>{
           if(error) throw error;
           console.log(result);
    })
})
conn.end();

Using a query in NODE JS with MYSQL

let config={
     host:'localhost',
     user:'username',
     password:'password',
     database:'database_name'
};
let user_id=1;

let conn= mysql.createConnection(config);
conn.connect( (error)=>{
    if(error) throw error;
    let sql="SELECT * FROM users WHERE id=?";
    conn.query(sql, [user_id], (error, results, fields)=>{
           if(error) throw error;
           console.log(results);
    })
})
conn.end();

Middleware in Express JS

Middleware is a function that has access to request objects and response objects.

Create middleware

let isLogin= function(req, res, next){
         console.log('Checking user is loginned or not.');
         next();
}

How to use middleware in express app

For all routes.

app.use(isLogin);

For single route

app.get("/user_dashboard", isLogin, (req, res,){
       res.send('Home page')
})

File upload using NODE JS middleware MULTER

Package: multer

Install

npm install multer

Load multer package

let multer= require('multer')

initialize multer

let upload= multer({
             storage: storage,
             fileFilter: filter,
             limits: { fileSize: 1024*1024}
}). single('file_input_element_name')

Define storage property

let storage= multer.diskStorage({
    destination:function(req, file, cb){
        console.log(file);
        cb(null, 'public/upload')
    },
    filename: function( req, file, cb){
        cb(null, Date.now()+"-"+file.originalname)
    }
});

Define filter property

let filter= function(req, file, cb){
    if(file.mimetype=="image/jpeg" || file.mimetype=="image/jpg" || file.mimetype=="image/png"){
        cb(null, true);
    }
    else{
        cb(new Error('Invalid file type, only jpeg, jpg, png files are allowed.'));
    }
}

Image upload route

app.post("/upload_image", (req, res)=>{
                 upload(req, res, (error)=>{
                                       if(error){
                                             return res.status(400).send({message: err.message});                                                
                                         }
                                       res.send("Image uploaded successfully.");
                  })
});

Express Session

Module

express-session

Install Module

npm install express-session

Load express session module

let session=require('express-session')

Use express session module

app.use( session({
    secret:"ctalmora", // will reduce the ability to hijack a session to only guessing the session ID
    resave:true,  // save back to store
    saveUninitialized:true  // Forces a session that is "uninitialized" to be saved to the store.  
}))

Create and use session

req.session.session_variable_name

Destroy session

req.session.destroy( (error)=>{
       if(error) throw error
       console.log('all session data destroyed');
}}

Express cookies

Module

cookie-parser

Install Module

npm install cookie-parser

Load cookie-parser

let cookieParser=require('cookie-parser');

Use cookie-parser

app.use(cookieParser())

Create or set cookie

res.cookie(cookie_name, value, {expires: new Date(Date.now()+ 3600000*24*30) })  // where 3600000 is milliseconds

res.cookie(cookie_name, value, {maxAge: new Date(Date.now()+ 3600000*24*30) })  // where 3600000 is milliseconds

Get cookie at client side (Browser)

document.cookie

Get cookie at server side

console.log(req.cookies.cookie_name)

Delete a cookie

res.clearCookie(cookie_name)

Restart Node JS app automatically when you changes on server using Nodemon?

Package

nodemon

Install nodemon

npm install nodemon -g

npm install nodemon --save-dev

Use nodemon

At package.json file

{
  "name": "newdata",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "start":"nodemon app.js",
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "body-parser": "^1.19.0",
    "cookie-parser": "^1.4.5",
    "ejs": "^3.1.6",
    "express": "^4.17.1",
    "express-session": "^1.17.2"
  }
}

Validation in express.js

Package

express-validator

Install Package

npm install express-validator

It is middleware that wrap validator.js and sanitizers.

Import express-validator

const {body, validationResult}=require('express-validator')

How to use

app.post("/login",
    body('email').isEmail(),
    body('password').isLength({min:8, max:20}),
(req, res)=>{ 
});

Get errors

let errors=validationResult(req); // will  return error object

Check errors is empty or not

.isEmpty()

Error methods

1. .array() : Return array of validation errors.
2. .mapped(): Return object, where the keys are field name and values are validation errors.

Use custom error messages

.withMessage(custom_message_string)

List of functions of validator

Sanitizers

Quicky create application skelton using express generator

npx express-generator --view=ejs 

where --view=ejs is setting view template ejs

Print property value whether property pass or not from controller to view (ejs)

<% if(typeof message !== 'undefined'){ %>
          <%= message %>
<% } %>