Category: Node.js

Node.js Overview

Node.js processing model

• Follows single threaded even loop processing model which can handle more and more concurrent requests easily
• Another important point to keep in mind that Node.js architecture has two types of threads

Main Thread (Single Thread)

• Called as internal thread as well, all the non I/O blocking requests are assigned using Main thread

Worker Thread(s)

• Used for assigning blocking I/O heavy requests

Here are the details on how the single threaded event loop based processing works

• Client sends the request to web sever
• Node.js web server receives client requests from different clients, puts them into a queue. This queue is called event queue
• Node.js has an internal component called event loop which runs the loop on event queue, assigns the request to a single thread if the request is non-blocking
• In case of blocking (I/O heavy) request, event loop will assign this to worker thread
• While worker thread is processing the request, event loop will continue to process other requests available in event queue

Node.js and Standard Webserver Flow-Diagramms

Node.js Flow Diagram
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Standard Webserver Flow Diagram
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• Reference: Node.js – Overview of Single Threaded architecture

My First Node.js Web Application

How it works ?

• Netbeans runs our Code in 2 Steps
• Step1: Netbeans start a nodejs server process to execute HTTP server Code
• –> Our HTTP server is now listening on port : 9900
• Step2: Netbeans starts a Chrome Browser Windows and connects to Port 9900
• –> Our Browser display the Content provided by our Http Server

Run a first Node.js Project

Setup a Node.js project properties within Netbeans

Step 1 : Configure Netbeans Project Run Methode	Step 2 : Configure Node.js Properties
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• Reference Node.js tutorial part 1: setting up your Netbeans environment

Add the following Code to main.js

const http = require('http');
const port = 9900;

const requestHandler = (request, response) => {
    let funcName = "requestHandler";
    if (request.method === 'GET' && request.url === '/' ){
        dumpMessage(funcName, "Request Method: GET - request URL: " + request.url);
        response.writeHead(200, {"Content-Type": "text/html"});
        response.end('Hello Node.js Server - at:  ' + getTime() + '!');
    }
};

const server = http.createServer(requestHandler);

server.listen(port, (err) => {
    let funcName = "server.listen";
    if (err) {
        return console.log(funcName, 'something bad happened: ' + err);
    }

  dumpMessage(funcName, 'server is listening on port: ' + port);
});

function dumpMessage(testName, mesg) {                                       
    console.log(getTime() + testName + ":: --> " + mesg);           
};
    
function getTime() {
    var ts = new Date();
    return ts.toLocaleTimeString()+ ":" + ts.getMilliseconds() + "  ";
};

Finally run the Node.js Code

Step 3 : Run the project
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Run above Node.js project manaully

Start the http Server

D:\xampp\htdocs\pvdata\testNodejs> "D:\Program Files\nodejs\node.exe"  "D:\xampp\htdocs\pvdata\testNodejs\main.js"
17:14:42:536  server.listen:: --> server is listening on port: 9900

Redirect your browser to the Listening Adress of our Web Server: http://localhost:9900

Browser Output
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Debugging a Node.js Application with Netbeans – Currently NOT working due to Netbeans Bug 271238

• Debugging the Node.js App with Netbeans 8.2 fails following Error
• This is unresolved NetBeans Bug 271238 – Node.js v8.1.3 cannot be debugged

"D:\Program Files\nodejs\node.exe" "--debug-brk=9292" "D:\xampp\htdocs\pvdata\testNodejs\main.js"
 (node:10116) [DEP0062] DeprecationWarning: `node --debug` and `node --debug-brk` are invalid. 
Please use `node --inspect` or `node --inspect-brk` instead. 

Done.

Debugging ourNode.js Application manually

Start the node.js process with inspect-brk option

• Enable inspector agent
• Listen on default address and port (127.0.0.1:9229)
• Break before user code starts

D:\xampp\htdocs\pvdata\testNodejs> node --inspect-brk main.js
Debugger listening on ws://127.0.0.1:9229/9391ed9f-a46d-4f49-bee2-b83d6dafb055
For help see https://nodejs.org/en/docs/inspector

Attach Chrome Devtools 55+ to the Node.js Debugger process

• Open a Chrome DevTool 55+ Browser session with following URL: chrome://inspect
• Select : Open dedicated DevTools for Node

Attach Chrome DevTools to Node.js Inspector
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CLI should respond with: Debugger attached

D:\xampp\htdocs\pvdata\testNodejs> node --inspect-brk main.js
Debugger listening on ws://127.0.0.1:9229/9391ed9f-a46d-4f49-bee2-b83d6dafb055
For help see https://nodejs.org/en/docs/inspector
Debugger attached.

Start Debugging

Debug Node.js by viewing Sources and setting Breakpoint
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• Reference: Node.js Debugging Guide

Reference

• Reference: Node.js – Overview of Single Threaded architecture
• Node.js tutorial part 1: setting up your Netbeans environment
• Node.js quick file server (static files over HTTP) using es6
• Node Hero – Your First Node.js HTTP Server
• Reference: Bug 271238 – Node.js v8.1.3 cannot be debugged
• Node.js Debugging Guide