Introduction

What is Node.js

JavaScript-based environment to create web-servers, networked applications or to perform helpful tasks e.g. minifying or concatenating

A free open source framework

Introduction > What is Node.js

Why Node.js

Can have lots of connections sending information simultaneously
​

Asynchronous I/O and non-blocking
 

It's fast, lightweight, efficient, and has ability to use JavaScript on both frontend and backend

Good for real-time applications
 

Serves as a proxy server

Introduction > Why Node.js

So what's this NPM?

Package Manager for installing libraries that extends Node with reusable components

NPM website

Introduction > So what's this NPM?

Difference Node.js & web JS

Node.js uses a different set of API's that are suitable for backend development

web JavaScript is limited with backend support due security reasons

Introduction > Difference Node.js & web JS

Installation

How to install

Download the latest version from the website

Run the installer

Follow the prompts in the installer

Restart your computer

Installation > How to install

Test the installation

Open Command Line tool

Use              to check if Node.js is installed and what version
 

Use              to check if NPM is installed and what version

Installation > Test the installation

node -v

npm -v

Create test file and run it

Create a file called test.js

Add                                                   to the file

Go to the Command Line and type         

Installation > Create test file and run it

console.log('Some random text here');

node test.js

Console

Methods

Console > Methods

let welcomeMessage = 'Hello World';
let errorMessage = 'Fail!';
let developer = { 
    favouriteLanguage: "JavaScript",
    age: 23
}


// Prints out 'Hello' to the console
console.log(welcomeMessage);


// Prints error message to the console
console.error(errorMessage);


// Prints out an object
console.dir(developer);

Read Eval Print Loop

What is REPL?

Read Eval Print Loop > What is REPL?

Represents a computer environment where a command is entered and the system responds with an output in an interactive mode

Can be started by typing in          in the console

node

REPL Commands

Read Eval Print Loop > REPL Commands

// Terminate the current command
ctrl + c

// Terminate the Node REPL
ctrl + c (twice) or ctrl + d

// Going through command history and modify commands
Up/Down keys

// List of current commands
tab

// List of all commands
.help

// Exit from multiline expression
.break or .clear

// Save the current REPL session to a file
.save filename

// Load file content in current REPL session
.load filename

Buffer

What is a Buffer?

Buffer > What is a Buffer?

Used to store binary data while reading data from a file or when receiving packages over the network

Options with Buffers:

• Create
• Read
• Write
• Concatenate
• Convert to JSON
• Compare

Examples

Buffer > Examples

// Creating a Buffer
let foo = new Buffer(10); // 10 = number of octets
let foo = new Buffer([25, 30, 35, 40, 45]);


// Reading a Buffer
buf.toString([encoding][, start][, end]) 
// start and end are index numbers


// Writing to Buffers
buf.write(string[, offset][, length][, encoding]) 
// length is number of bytes to write


// Concatenating
Buffer.concat(list[, totalLength])


// Convert to JSON
buf.toJSON()


// Compare Buffers
buf.compare(otherBuffer);

Global objects

What are they?

Global objects > What are they?

Objects that are already included in all available modules

Can be:

• Modules
• Functions
• Strings
• Objects

Examples

Global objects > Examples

// Print information
console


// Get information about the current process
process


// Run callback cb after x milliseconds
setTimeout(cb, ms)


// Stops the timer that was set with setTimeout
clearTimeout(t)


// Runs callback repeatedly for x milliseconds 
setInterval(cb, ms)


// The filename of code that is being executed
console.log(__filename);


// The directory of the script that's executing
console.log(__dirname);

Streams

What are Streams?

Streams > What are Streams?

Objects that let you read data from a source or write data to a destination

4 type of streams:

• Readable
• Writable
• Duplex
• Transform

Each type is an EventEmitter instance and throws several events, such as data, end, error and finish

Process

What is it?

Process > What is it?

Every script runs in a process

Every process includes a process object to get all information and control about the current process

Events

Process > Events

// Emitted when the event loop is empty and there is nothing in schedule
beforeExit


// Emitted when the process is about to exit
exit


// Emitted when an exception goes back to the event loop
uncaughtException

Callbacks

What is a Callback?

Callbacks > What is a Callback?

An asynchronous equivalent for a function

It's called at the completion of a task

Blocking call

Callbacks > Blocking call

The script blocks until it reads the file and then only it proceeds to end the program

const FS = require("fs");

let data = FS.readFileSync('test.txt');

console.log(data.toString());
console.log('The end');


// Output: The data from test.text followed by "The end"

Non-blocking call

Callbacks > Non-blocking call

The script doesn't wait, it proceeds to print to the console while the script still continues reading the file.

const FS = require("fs");

FS.readFile('test.txt', function (err, data) {
    if (err) return console.error(err);
    console.log(data.toString());
});

console.log('The end');


// Output: "The end" followed after by the data from test.txt

Modules

What is a Module?

Modules > What is a Module?

A set of functions

You can create your own Module and include
it in your application

Types of Modules:

• Core
• Local
• 3rd party

Core Modules

Modules > Core Modules

// Creating a HTTP server (includes classes, methods and events)
http


// URL resolution and parsing (includes methods)
url


// Dealing with query strings (includes methods)
querystring


// Dealing with file paths (includes methods)
path


// Working with file I/O (includes classes, methods and events)
fs


// Utility functions
util

Include a Core Module

Modules > Core Modules > Include a Core Module

const FOO = require('core_module');

Local Modules

Modules > Local Modules

Locally created modules in your application

Can include different functionalities separated in files and folders

Loading a Local Module

Modules > Local Modules > Loading a Local Module

const FOO = require('local_module');

Event Loops

What are Event Loops?

A main loop that listens for events

Triggers a callback function when an event is detected

There are multiple in-built events which are used to bind events and event listeners

Event Loops > What are Event Loops?

EventEmitter

All objects which emit events are the instances of events.EventEmitter

EventEmitter class is within the events module

Event Loops > EventEmitter

// Use require (or import) to import the module
const EVENTS = require('events');

// Creating an eventEmitter object
let eventEmitter = new EVENTS.EventEmitter();

Events

Event Loops > EventEmitter > Events

// Event emitted when a listener is added
newListener

// Event emitted when a listener is removed
removeListener

Methods

Event Loops > EventEmitter > Methods

// Returns an array of listeners
listeners(event)


// Adding a listener at the and of the listeners array
addListener(event, listener)


// Adding a listener at the end of the listeners array
on(event, listener)


// Removes all listeners
removeAllListeners([event])


// Removing a listener from the listener array
removeListener(event, listener)


// Adding a one time listener to the event
once(event, listener)


// EventEmitters will give a warning if more than x 
// (usually 10) listeners are added to an event
setMaxListeners(n)

File system

What is it?

File system > What is it?

Using simple wrappers around POSIX functions using File I/O

Can be imported using the require method
 

fs module has synchronous and asynchronous forms

Asynchronous is recommended since it's non-blocking

File methods

File system > File methods

// Opening a file
fs.open(path, flags[, mode], callback)


// Getting information from a file
fs.stat(path, callback)


// Closing a file
fs.close(fd, callback)
// fd = file descriptor returned by fs.open()


// Reading a file
fs.read(fd, buffer, offset, length, position, callback)
// fd = file descriptor returned by fs.open()


// Writing to a file
fs.writeFile(filename, data[, options], callback)


// Deleting or truncating a file
fs.unlink(path, callback) // Deleting
fs.ftruncate(fd, len, callback) // Truncate

Directory methods

File system > Directory methods

// Create a directory
fs.mkdir(path[, mode], callback)
// Mode = permission


// Read a directory
fs.readdir(path, callback)


// Delete/remove a directory
fs.rmdir(path, callback)

Debugging

Core debugger

Debugging > Core debugger

const FS = require('fs');

FS.readFile('test.txt', 'utf8', function (err, data) {

    // Built-in non-graphic debugging tool
    debugger;

    if(err) throw err;

    console.log(data);
});

Run the following command:             

node debug app.js

Commands

Debugging > Core debugger > Commands

// Add the variable or expression into watch
watch

// See the values of what you have added into watch
watcher

// Pause the running code
Pause

// Stop at the next statement
next

// Step in function
step

// Step out of function
out

// Continue to execute and stop at the debugger statement
cont

Example

Read data

Example > Read data

// file.txt

Michael A 2
Jeroen B 2
Nando C 1
Nick B 8
Ruben D 5

// Load the fs (filesystem) module
const FS = require('fs');

// Reads the contents of the file
FS.readFile('file_log.txt', function (err, logData) {

    // Displays an exception and end app if an error occurred
    if (err) throw err;
  
    // logData is a Buffer, then converts to a string
    let text = logData.toString();
});

Add parsing data

Example > Add parsing data

// Load the fs (filesystem) module
const FS = require('fs');

// Reads the contents of the file
FS.readFile('file_log.txt', function (err, logData) {

    // Displays an exception and end app if an error occurred
    if (err) throw err;
  
    // logData is a Buffer, then converts to a string
    let text = logData.toString();

    let results = {};

    // Break up the file into lines.
    let lines = text.split('\n');
  
    // Go through every line
    lines.forEach(function(line) {
        // Divides the string with a space
        let parts = line.split(' ');
        // Selects the second item of the Array
        let name = parts[0];
        // Selects the third item of the Array
        let count = parseInt(parts[2]);
    
        if(!results[name]) {
            results[name] = 0;
        }
    
        results[name] += parseInt(count);
    });
  
    console.log(results);
});

Resources

Useful links

Node.js ES5+ support

Awesome Node.js

Self-guided workshops

Resources > Useful links