Introduction to JavaScript

Vladimir de Turckheim

Lead Node.js engineer @ Sqreen​ (ex. Steamulo, Secway)

A bit of history

Timeline

Key dates

  • 2006: JQuery
  • 2009: Node.js
  • 2009: AngularJS
  • 2013: React
  • 2016: Angular 2

Weird stuff

  • ActionScript
  • TypeScript
  • CoffeeScript

JavaScript is a multi-paradigm programming language which syntax inherits from C with weak duck typing.

This should be enough for you to write JavaScript actually.

Paradigms

  • Imperative
  • Object oriented (prototypes)
  • functionnal

Where to run JavaScript

In the browser

Console

  • Press F12
  • Find the Console
  • Write JS

In a file

<html>
    <body>
        <script> // write code here </script>
    </body>
</html>

All browser do not support all versions of JS...

On your computer

Install Node.js

DOC

The best Fr/En doc is the mozzilla one:

https://developer.mozilla.org/fr/docs/Web/JavaScript/Reference

Browser support is also indicated there.

Basics

Hello world

// Hello World
alert('hello World');

// in console
console.log('hello world');

Comments

// This is a one line comment

/*
this
is
a
multi
line
comment
*/

variable declaration and types

var a; // a has the undefined value here. 
// undefined is a special value in js that means, that what your are looking for is not here.
var b = 1; // b is a number 
var c = 1.1; // c is a number
var d = "hello"; // d is a string
var e = 'hello'; // e is a string
var f = function () {}; // f is a function
var g = {}; // g is an object
var h = null; // h is the null object
var i = NaN; // i is the Not a Number value which is a number
var j = []; // j is an array
var k = true; // k i a boolean

const X = 1; // I am a constant
let y = 2; // I can be changed

Pleas place semicolons (;) even if they are optional
// The typeof keyword is used to check the type of a variable
> typeof a
    undefined
> typeof b
    'number'
 '>' means I write this in the js console, the next line is the output of the command

Boolean manipulation

// Equality
var x = 1;
var y = '1';
x == y // true
x === y // false
// when using the ==, a type casting is made.

// Comparison:
var a = true;
var b = false;
a || b // true: a OR b
a && b // false: a AND b

// Negation
!true === false

Boolean manipulation

// falsy values
// The following values are casted as false in boolean equations:
false
''
""
NaN
null
undefined
0

// all other value resolve to true.

// Special usage of boolean operators:
var a = 1;
var b = 0;
var c = b || 1; // c is 1;

// casting to a boolean
var d = 1;
!!d === true;

// checking the existence of something
if(something) {

}

if, for, while

if (test) {
    // do stuff
} else if(other test) {
    // do other stuff
} else {
    // to other other stuff
}

for(var i = 0; i < 1000; i++) {
    // do stuff
}

// variables are not scoped, i exists here too
> i
    1000

while (test) {
    // ditto
}

Objects

In JS, all objects are dicts:

var a = {
    key: 'value',
    key2: 2
};

a.key === 'value';
a['key2'] === 2;

// you can add claims to the object

a.key3 = 10;
a['key4 weird'] = { a: 1};

> a
    { key: 'value', key2: 2, key3: 10, 'key4 weird': { a: 1} }

> a.pony
    undefined

Arrays

// Arrays are created with the [] symbols
var a = [1, 'a', {}];
> a[0]
    1

a[5] = 10
> a
    [ 1, 'a', {}, , , 10 ]
> a[4]
    undefined

// get length:
> a.length
    6

// add something at the end of an array
var b = [];
b.push(1) // b === [1]
var x = b.pop(); // x === 1; b is []

// concat: it returns a new array;
var c = ['c'];
var d = ['d'];
var e = c.concat(d); // c is ['c']; d is']; is ['c','d'];

Functions

// Functions are declared with the `function` keyword

function f (a) { // the name of the function is f
    return a + 1;
}

// or
var g = function (a) {
    return a + 1;
}
// the function held in the g variable does not have any name, 
// it is said to be anonymous

f(1) === 2;
f('a') === 'a1';

// Arrow functions
g = (x) => x + 1;

Functions (callbacks)

// Some methods in javascript take a function as parameter
// the method 'map' on arrays:

var a = [1, 2, 3, '4'];
var b = a.map(function (item) { return item + 1; }); 
> a
    [ 1, 2, 3, '4' ]
> b
    [ 2, 3, 4, '41' ]

// the anonymous function passed as argument to map 
// has been called on all items of a and a new array has been created

Methods on arrays

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array

Can you:

  • sort an array
  • find an element in an array
  • filter an array
  • ... ?

Classes

// this function is called a constructor
class Person {

  constructor (name, age) {
    
    this.name = name;
    this.age = age;
  }
  
  sayHello() {
    return 'Hello, my name is ' + this.name;
  }
}

var john = new Person('john', 20);

> john.sayHello()
    'Hello, my name is john'

> john instanceof Person
    true

DOC

The best Fr/En doc is the mozzilla one:

https://developer.mozilla.org/fr/docs/Web/JavaScript/Reference

Browser support is also indicated there.

GOOGLE:

"mdn tri liste" :

first result:  Array.prototype.sort()

JSON

JSON is a format used to exchange data

JSON stands for JavaScript Object Notation

In the real world

{
    "key": "value",
    "key2": { ... }
}

OR
[1, 2, { ... }]


{...} means any JSON object.
// In js:

var a = { a: 1, b: { c: "c" } };
var aJson = JSON.stringify(a);
var b = JSON.parse(aJson);

> a
    { a: 1, b: { c: 'c' } }
> aJson
    '{"a":1,"b":{"c":"c"}}' // this is a string !
> b
    { a: 1, b: { c: 'c' } }
> a == b
    false

JQuery & DOM manipulation

JQuery is a JS library that provides an uniform api on all browser and make HTML (DOM) manipulation easier

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Title</title>
        <script src="https://code.jquery.com/jquery-3.1.0.js"></script>
    </head>
    <body>
        <div id="main">
            <p>hello World</p>
        </div>
        <script src="index.js"></script>
        </body>
</html>
  • JQuery is imported in the headers
  • Our script is imported in body

Ugly part: in our script the $ contains JQuery...

$('#main').click(function () {
    $('.second').text('hello'); 
    // we select all items whose class is 'second' (the . means class) and change their 
    // text to 'hello';

    $('#main').css('background-color', 'yellow');
    // we change the color of the element whos id is 'main' (the # means id)
});


// AJAX call
var settings = {
  "async": true,
  "crossDomain": true,
  "url": "http://petstore.swagger.io/v2/pet/findByStatus?status=available",
  "method": "GET",
  "headers": {
    "accept": "application/json"
  }
}

$.ajax(settings).done(function (response) {
  console.log(response);
});

index.js

RTFM

LMGTFY

Good places to find help

  • StackOverflow
  • Github issues

Please do not open an issue unless you have googled your problem for at least 2 hours !!

Workshop

  1. Get the base project (previously on this pres)
  2. Start it and reproduce what we did in the slides
  3. Go to http://petstore.swagger.io/#!/pet/findPetsByStatus
  4. From the starter project and with the help of the online documentation create a page with:
  • 3 buttons: "available", "pending", "sold"
  • When we click on them, it displays the list of pets by status

Introduction to JavaScript

By Vladimir de Turckheim

Introduction to JavaScript

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