Linnaeus University

License for this work

This work is produced by John Häggerud at Linnaeus University.

All content in this work excluding photographs, icons, picture of course literature and Linnaeus University logotype and symbol, is licensied under a
Creative Commons Attribution 4.0 International License.

You are free to

• copy and redistribute the material in any medium or format
• spread the whole or parts of the content
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• convert the content to another format
• change the content

If you change the content do not use the photographs, icons, picture of the course literature or Linnaeus University logotype and symbol in your new work!

At all times you must give credit to: ”Linnaeus university” with the link https://webbprogrammerare.se and to the Creative Common-license above.

The Philosophy

• Small core
  • core modules like http, fs, utils...
• Userland modules
• Small modules, doing one thing well
• Package managers like npm, yarn

const http = require('http') // core module
const thirdPartyModule = require('someThirdPartyModule') // installed module 
const myLocalModule = require('./lib/myLocalModule') // own local module

ECMAScript modules? https://nodejs.org/api/esm.html

Characteristic

• Single threaded architecture
• Non-blocking
• Asynchronous
• Event-driven

Multi-Thread web server architecture

• Isolated "process" for each request
  • More traditional web servers like Apache (PHP), Tomcat (JAVA)
• Having a thread pool and use a thread for each request
  • Wait for available threads, taking system RAM
  • Lots of idle in each thread, waiting for I/O operations, context switching
  • Synchronous programming model
  • Problem handling many simultaneous requests

Single-threaded web server architecture

Blocking vs. Non-blocking

Blocking

<?php
  $homepage = file_get_contents("http://www.example.com");
  echo $homepage;

  // Must wait to do stuff here...
?>

Non-blocking - asynchronous - Callback pattern

let request = require("request")

request('http://www.example.com', (error, response, body) => {
  if (!error && response.statusCode === 200) {
    console.log(body) // Show the HTML for the homepage.
  }
  ...
})
// ... don't have to wait to do stuff here

Event-driven programming

• Callbacks
• Promises
• Async/Await
• Event Emitters
  • Create your own events
  • Listen for multiple triggers of events

When to use Node.js

• Javascript everywhere!
  • Client-side, JSON as data format, Server-side, (from database)
• Server-side web applications
  • Traditional dynamic web site
  • Backend for Single Page Application
    • Web APIs serving JSON format
    • Front-end servers
• Realtime applications
  • Handling realtime event from server to clients

When NOT to use Node.js!

• Running code that blocks the thread
• Not suited for requests that handles CPU-intensive tasks
  • Tasks involving calculation
  • Use clustering to offload all heavy computation to background services
    • There is a cluster module in Node.js

Be aware!

let requestHandler = (req, res) => {
  let body = req.body // Contains the POST body the client sends
  try {
     let json = JSON.parse(body)
     res.end(json.user.username)
  }
  catch(e) {
     res.end("FAIL")
  }
}