JavaScript Core

JavaScript
Core
Nicolas Demengel and François Sarradin

Application
(client side) Web Page
Animation

HTLM(5)
CSS(3)
Client
JavaScript Server
JS
Engine

Service
(server side) Embeded
(noSql, ...)

JavaScript
History

1996 1998
1995 1997 2000 2010 What's next?

ECMA 1.3
1.0, 1.1 1.5 1.8.5 ES 6
ES 3 ES 5 Harmony
ECMAScript
Brendan Eich 1.2
@ Netscape
JavaScript

JavaScript
Is made of...

Self Python Perl C/Java

JavaScript

ActionScript Dart CoffeeScript

JavaScript

Language
&
Concepts

JavaScript Syntax
Looks like Java / C++
/* Factorial of n. */
function fact(n) {
// result of fact
var result = 1;
for (var i = 1; i <= n; i++) {
result *= i;
}
return result;
}

JavaScript
Is dynamically typed
var x = 1; // it should be an int
var s = "a"; // string or char?

// it's a function, (type of p?
// does it return something?)
function f(p) { /* ... */ }

var g; // anything (even a function)

JavaScript
Has bad parts
42 == '42' !== 42
if (false) <-> if (null) <-> if (undefined)
false != null == undefined
false !== null !== undefined

return
{
prop: "val"
};

Use an editor providing validation with JSLint

JavaScript
Has few built-in types
● Boolean true / false
● Number 42 21.6 NaN +∞ -∞
● String "hi" 'hello'
● Date java-like
● Regexp /^.*([0-9]+)w{2,3}$/
● Object {prop: val}
● Array [a, b] (it's just an Object)
● Function function() {}

● List, Map, Set: where are you? => ES 6

JavaScript
Can define functions
// function declaration (statement)
function f(x) { /* ... */ }

// function expression (operator)
var f = function(x) { /* ... */ };

// Function constructor
var f = new Function('x', '...');

JavaScript
CAN HAZ FUNCTIONZ EVERYWHERE
function compose(f, g) {
// BTW, this is a closure!
// more on that later
return function(x) {
return f(g(x));
};
}

compose(square, add_one)(10);

JavaScript
Function: scope & binding
var o = {
name: "an object",
logName: function() { log(this.name); }
};

// o.logName can be assigned to a variable:
var logN = o.logName;
logN();

// another way to give o the logName method
function ln() { log(this.name); }
var o = { name: "an object" };
o.logName = ln;

JavaScript
// what is the value of 'this'?
var o = { /* ... */
logName: function() { log(this.name); }
};

// here it obviously refers to o
o.logName();

// what about the following?
function ln() { log(this.name); }
ln(); // er...

JavaScript
● this = object to wich the function is bound
○ By default: the global object (window in browsers)

● Change the way a function is bound to an
object: apply or call

JavaScript
var o = { nm: "John Doe" };

function say(message) {
console.log(this.nm + ": " + message);
}

say("hello!"); // ": hello!" (this.nm is undefined)

o.sayIt = say;
o.sayIt("greetings!"); // "John Doe: greetings!"

say.call(o, "yo!"); // "John Doe: yo!"
say.apply(o, ["hi!"]); // "John Doe: hi!"

JavaScript
Function arguments
(function(x, y) {
console.log(y); > 'b'

console.log(arguments.length); > 3
console.log(arguments[2]); > 'c'

console.log(arguments.callee);> function(){ }

console.log(arguments.join); > undefined
// Array.prototype.join.call(arguments)

})('a', 'b', 'c');

Prototype-oriented programming
Languages

Self

NewtonScript JavaScript Lua Io

Ioke
JVM

Instance, prototype, and inheritance
var Vehicle = {
description: "some vehicle",
startEngine: function() {
console.log(this.description
+ " => engine started");
}
};
// uses Vehicle as proto
var Car = Object.create(Vehicle);
Car.description = "some car";
Car.wheelCount = 4;

What do you get?
Vehicle.startEngine();
> "some vehicle => engine started"

Car.startEngine();
> "some car => engine started"

console.log(Vehicle.wheelCount);
> undefined

console.log(Car.wheelCount);
> 4

Inheritance manipulation
Car.startEngine = function() {
console.log("overridden");
}
Car.startEngine(); > "overridden"

// let's delete the car-specific method
delete Car.startEngine;

// parent method is still there
Car.startEngine(); > "some car => engine started"

JS prototype-based programming
= delegation (object ⇒ prototype)

Inheritance: level 2
Car.startEngine = function() {
Vehicle.startEngine.call(this); // ≃ super.start
console.log("model: " + this.model);
}

// inheritance is not limited to one level
var myPigeot = Object.create(Car);
myPigeot.description = "My Pigeot";
myPigeot.model = "403";

myPigeot.startEngine();
// My Pigeot: engine started
// model: 403

Classes in JS?

Vehicule
Car

myPigeot

Vehicle, Car = prototypes ≃ classes
Note: myPigeot can be prototype too!


Wait!...

What about that Object.create()?

Create an instance
// Object.create(): JS 1.8.5 and +
if (!Object.create) {
Object.create = function(o) {
// creates new temp. constructor
function F() {}

// gives it o as prototype
F.prototype = o;

// instantiates
return new F();
};
}

Classes in JS
// previous example could have been written:
var Vehicle = { /* desc, startEngine */ };

function Car(desc) { this.description = desc; }

Car.prototype = Vehicle;

Car.prototype.description = "some car";
Car.prototype.wheelCount = 4;

var myPigeot = new Car("My Pigeot");
myPigeot.model = "403";

New in JS
Er... Car is a functions, but I can new it?!

● new is a keyword that
1. Allocates an object
2. Inits this object with constructor

● new Car("some car") is equivalent to
var car = {};
car.__proto__ = Car.prototype;
Car.call(car, "some car");

Last word about constructor functions
What happens when calling the Car
constructor without new?

this is bound to global object

Want to play this game?
○ Change window.location and you'll risk a crash

Last but not least
● Be carefull with this and new

● Factory method instead of new
function createCar(d) { return new Car(d); }

● Prevent bad usage of your constructor
function Car(desc) {
if (!(this instanceof Car)) {
return new Car(desc);
}
/* ... */
}

Private members
var Entity = (function() { // class lvl
var counter = 0; // private

return function() { // instance lvl
var id = counter++; // private

this.getId = function() {
return id;
}
};
})();

Private members
var o1 = new Entity();
var o2 = new Entity();

console.log(o1.id);
> undefined

console.log(o1.getId());
> 1

console.log(o2.getId());
> 2

Access to Your Web Page
DOM manipulation
DOM != JS, it's another API

No need for jQuery
○ getElementById()
○ getElementByTagName()
○ getElementByName()
○ getElementByClassName() // !IE
○ querySelector() // IE 8
○ querySelectorAll() // IE 8

Access to Your Web Page
DOM manipulation: tips

● know your CSS selectors
○ #element
○ .element
○ [attribute=value]

● limit changes to the DOM
○ use fragments

The Good, The Bad, and The Ugly

References
Books
David Flanagan, JavaScript: The Definitive Guide, 6th
Edition, O'Reilly Media, April 2011

Doug Crockford, JavaScript: The Good Parts, O'Reilly
Media, May 2008

References
Online
Doug Crockford, JavaScript: The Good Parts
http://googlecode.blogspot.com/2009/03/doug-crockford-
javascript-good-parts.html

Alex Russel, Learning to Love JavaScript
http://www.google.com/events/io/2011/sessions/learning-to-
love-javascript.html

John Resig, Learning Advanced JavaScript
http://ejohn.org/apps/learn/

Mozilla, JavaScript Reference
https://developer.mozilla.org/en/JavaScript/Reference/

JavaScript Core

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