CS6320:  SW Engineering of Web Based Systems
Instructor Outline Syllabus Projects Links  

 

NodeJS

What is NodeJS and what is MEAN

NodeJS = asynchronous event driven JavaScript runtime, Node is designed to build scalable network applications. In the following "hello world" example, many connections can be handled concurrently. Upon each connection the callback is fired, but if there is no work to be done Node is sleeping

*******It has a built in HTTP server library --- you don't need a separate web server like Apache --- the nodeJS application can do the http listening -----***********************

simple NodeJS application that is an http listener and always returns Hello World

const http = require('http');
const hostname = '127.0.0.1';
const port = 3000;
 const server = http.createServer((req, res) => {
    res.statusCode = 200;
    res.setHeader('Content-Type', 'text/plain');
    res.end('Hello World\n');  });

 server.listen(port, hostname, () => {
    console.log(`Server running at http://${hostname}:${port}/`);
  });

This is in contrast to today's more common concurrency model where OS threads are employed. 

  • Created by Ryan Dahl in 2009
    • Development && maintenance sponsored by Joyent
    • Licence MIT
    • Last release : 0.10.31
    • Based on Google V8 Engine
    • +99 000 packages

WHY NodeJS?

  • Asynchronous i/o framework

    • can be faster as event driven

    • can process more requests / second that competitors like RoR and Java

  • Single Thread with Event Loop-->speed

  • many many modules

    1 Language for Frontend and Backend

  • There are a number of NodeJS frameworks that extend its capabilities and help with MVC
    (i.e. Express, Meteor)

    There are a couple of implications of this apparently very simple and basic model

    •Avoid synchronous code at all costs because it blocks the event loop
    •Which means --> create callbacks!!!!!!!


When do you use NodeJS

● Web application

● web socket app

● Ad server

● Proxy server

● Streaming server

● Fast file upload client

● Any Real-time data apps

● Anything with high I/O

● chat/messaging

● realtime applications

● high concurrency applications

● communication hubs

● recommendation systems

● MORE MORE MORE

 

 

 

 

 

 

First -- Learn basic syntax of Javascript - see CS3520

from CS3520 website (client based but, syntax the same)

 

 

 

NodeJS basics

we will learn as we go..do recommended reading

 

 

 

NodeJS modules

  • Many NodeJS programs leverage the use of module (think of this like libraries or packages in other languages)
  • A module encapsulates related code into a single unit of code. (like packages in Java)
  • You can use other peoples modules or create your own

2 Ways to create a module

 
module.exports = {
    sayHelloInEnglish: function() {
      return "HELLO";    },
    sayHelloInSpanish: function() {
      return "Hola";    }
  };
 
// greetings.js  
 var exports = module.exports = {};
 exports.sayHelloInEnglish = function() {
    return "HELLO";  };
 exports.sayHelloInSpanish = function() {
    return "Hola";  };

 

how to import (require) a module into a NodeJS file

// main.js
                var greetings = require("./greetings.js");

// "Hello"
  greetings.sayHelloInEnglish();

// "Hola"
    greetings.sayHelloInSpanish();
The keyword require returns an object, which references the value of module.exports for a given file

 

how to install a module in your application director

$npm install <module name>

 

 

Installation, Application Setup and using Heroku

 

using NodeJS to connect and use a MongoDB database

 

 

© Lynne Grewe