Javascript IntroductionVu Viet Phuong - Portal Team

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Objective

• Help to approach Javascript easier

• Prepare to work with eXo javascript framework

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Subject

• Characteristic of Javascript language

• OOP with Javascript

• Javascript and DOM

• Ajax

• Javascript performance

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Characteristic of Javascript language

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What is Javascript ?

Netscape initially introduced the language under the name LiveScript in

an early beta release of Navigator 2.0 in 1995

Some characteristics :

- Script language

- Interpreted

- Changing rapidly and Cross-platform support is not consistent

JavaScript is the most popular scripting language on the internet

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What can We do with it ?

Provide interactive content on your Web pages(embeded in HTML page using <script> tag)

Much of its power is derived from both the built-in and document objects provided by the browser

Control Document Appearance and Content : document.write(), DOM...

Control the Browser : window.alert(); window.open(); window.close()...

Interact with the User : ability to define "event handlers"

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What Javascript can’t do

Javascript are confined to browser-related and HTML-related tasks

→ it does not have features that would be required for standalone languages

Some lack of features :

Graphics capabilities

Reading or writing of files

Multithreading, except whatever comes implicitly from the web browser's internal

use of threads

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Quick introduction of basic programming

JavaScript is similar to so many other languages: Arithmetic and logical operators are part of the languageFlow-control constructs such as if, while, and switch

Example :- Arithmetic Operators : + - * / % The addition operator (+) has a different behavior

when operating on strings as opposed to numbers

- Comparison Operators : > < >= <= != == === alert(“10” == 10) //display truealert(“10” === 10) //display false

- typeof operator :alert(typeof “some string”); //display string

http://www.techotopia.com/index.php/JavaScript_Operators

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Quick introduction of basic programming

Flow control : (if-else, switch)if (expression)

statement; else

statement;

Loops : (while, do-while, for) Loop control (break and continue)

Object-Related Statements:with Statement : a shorthand notation when referencing objects

with(document) {write(“Hello World”);}

for…in : used to loop through an object’s propertiesfor (pros in document) {document.write(pros);}

http://en.wikipedia.org/wiki/JavaScript_syntax

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Quick introduction of basic programming

Script Execution Order : interpreted line by line as it is found in the page

Case Sensitivity : JavaScript is case-sensitive: keywords, operators....

Statement Delimiters : Semicolons and Returns

Declare Variables :

- var keyword

- implicit declaration

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Data type

Data Type :

- Primitive data types: number, string, boolean, undefined, null

- Composite types: objects, arrays, and functions

Dynamic Typing : Type is inferred from the variable’s content

var test = “10”; //It's a string

test = 10; //It's a number now

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Data type

Automatic Type Conversion : Most powerful features of JavaScript, as well

as the most dangerous for the sloppy programmer

window.alert(“10” - 3); → result : 7

Force the conversion using methods like toString() or parseInt()

DynamicTyping.html

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Functions

Function creation syntax : function Add(x, y)

{ var sum = x + y; return sum; }

var test = new Function(“alert('test')”);

var test = function() {alert('test')};

How to deal with arguments :

– length property

– arguments[] property

FunctionCreation.html

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Context, Scope and Closures

Context : always be in some form on context (an object within which it's operating) the way context works is through the this variable

Closures : Inner functions can refer to the variables in their outer enclosing function

Curring effect

Hide variables from global scope

Scope : is tricky feature. In Javascript, scope is kept within functions

Context.html

Scope.html

Closures.html

http://jibbering.com/faq/notes/closures/

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Object-Oriented Programming with JavaScript

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Object in Javascript

Objects are the fundamental units of JavaScript

EVERYTHING except primative type in JavaScript is object

There are three object categories in JavaScript: • Native Objects• Host Objects• User-Defined Objects

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Object creation

1. Using new Object()

employee = new Object()

employee.name = "Tim";

employee.say = function() {

alert('hello');

}

2. Using Literal Notation

employee = {

name : "Tim",

say : function() {

alert('hello')

}

};

NOT reusable- we cannot easily initialize different versions of the created object

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Object creation

3. Object Constructor :

- Regular JavaScript function

- The difference is that, it is called via 'new' operator, without this, it just

likes other javascript method

// it to the current context function User( name ) {

this.name = name; }

// Create a new instance of that functionvar me = new User( "My Name" );

3. Object Constructor :

- Regular JavaScript function

- The difference is that, it is called via 'new' operator, without this, it just

likes other javascript method

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Object creation

Now, since User() is just a functionwhat happens when we treat it as such?

User( "Test" );

// Since its 'this' context wasn't set // it defaults to the global 'window' alert( window.name == "Test" ); // display true

ObjectCreation.html

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Prototype

Prototyping is the key to understanding the inheritance concept

“prototype” is a property of every function. Since constructor is also function, it's a property of constructor too

function User(){}; var test = new User();User.prototype.say = function() {alert('hello')};

test.say(); //display hello

ObjectCreation_Prototype.html

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Inheritance

Inheritance is the ability to have properties from “Super Class”

Set prototype property of constructor to an “super class” object

→ “sub class” object will have access to “super class” properties

function SuperClass() {this.superHello = function() {alert(“super hello”)}

}function SubClass(){}SubClass.prototype = new SuperClass();

Inheritance.html

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Encapsulation

Objects interact with each other via call method, and don't know what is happening inside

Private : only accessible to other private methods or privileged methods

function Bean() {var name = "test";

//Getterthis.getName = function() {return name};//Setterthis.setName = function(newName) {name = newName};

}

Encapsulation.html

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Polymorphism

Polymorphism : is a programming language feature that allows values of different data types to be handled using a uniform interface

In java, we can achieve this by implementing an interface

In weakly typed languages like JavaScript, types are implicitly polymorphic

http://en.wikipedia.org/wiki/Polymorphism_in_object-oriented_programming

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Namespace help us to avoid name conflic

Javascript, natively doesn't provide namespace feature

Namespacing

Workaround for this :

var = { DOMUtil : { },

….};

//After define DOMUtil, we use it in namespace like thateXo.core.DOMUtil = new DOMUtil() ;

Namespace.html

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Javascript and DOM

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DOM : Document Object Model

Dom is programming interface for HTML and XML documents

It provides a structured representation of the document

Javascript and DOM

<html><head>...</head><body>

<h1>Hello World!</h1></body>

</html>

// Does not work! → text is also consisdered a node document.documentElement.firstChild.nextSibling.firstChild

DOMExample.html

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There are a number of possible values

The three that you’ll encounter the most are the following:

Element (nodeType = 1), Text (3), Document (9)

Node types

http://www.javascriptkit.com/domref/nodetype.shtml

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API

document and window objects are the objects whose interfaces you generally use most often in DOM programming

window object represents the window itselfwindow.alert(); window.open(); window.scrollTo()

document property of window points to the DOM document loaded in that window

http://www.w3schools.com/jsref/obj_window.asp

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document

The document provides methods for creating and manipulating all of the document's child nodes, or elements

Creating and Retrieving elements: document.getElementById(id), document.createElement(name)

Get and Set Attributes:document.getAttribute(name), document.setAttribute(name,val)

https://developer.mozilla.org/en/Gecko_DOM_Reference

Document.html

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CSS

There are two problems that you encounter when working with CSS properties on DOM elements

Second, can't get pre-set style. We must get the computed style

First, JavaScript requires that you specify the unit of size for setting any dimensional property

document.getElementById(“table”).style.width = “200px”;

StyleTest.html

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DOM Event

Events are actions on DOM that can be detected by JavaScript

Every element on a web page has certain events which can trigger JavaScript functions

Examples of events:

- A mouse click - A web page or an image loading - Mousing over a hot spot on the web page

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Event Phases

Javascript events are executed in 2 phases

Capturing : event moving down the DOM tree to the element that instantiated event

Bubbling phase traverses up DOM tree to the root element

Bubbing.html

Capturing.html

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Event object

Contains contextual information about the current event

IE’s implementation is different from the W3C’s specification

function eventHandler(evt) {var e = window.event || evt;...

}

Default behaviour : Browser has some default actions that will always occur

click <a> element → redirect to other pagepress key on textbox → display chars on textbox

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Control event

Overriding the Browser’s Default Action :if ( e && e.preventDefault )

e.preventDefault();else

//IEwindow.event.returnValue = false;

Stop bubbling : if ( e && e.stopPropagation )

e.stopPropagation();else

window.event.cancelBubble = true;

OverrideDefaultAction.html

StopBubbling.html

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Event handler

Traditional Bindingdocument.body.onclick(handler);

W3C method of binding event handlersdocument.body.addEventListener('click', handler, false);

IE’s methoddocument.body.attachEvent('onclick', myKeyPressHandler);

https://developer.mozilla.org/en/DOM/event

Ajax

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Definition

Ajax (Asynchronous JavaScript and XML)

AJAX uses a combination of:

DOM

XMLHttpRequest

XML is sometimes used as the format for transferring data between the

server and client, although any format will work

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How it work

Request process can be handled asynchronously Then a SMALL portion of desired results can be loaded upon completion

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Make request

Create XMLHttpRequest Object- Internet Exployer 5, 6:

new ActiveXObject("Microsoft.XMLHTTP");

- IE7+, Firefox, Chrome, Opera, Safari : new XMLHttpRequest();

Establishing a Connection : GET or POST request// Open the socket ajx.open("GET", "/some/url", true); // Establish the connection to the server ajx.send();

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Send data Serializing Data:

function User() { name: "John", last: "Resig" }

// Serialized form serObj = name=John&last=Resig

Request method : GET ajx.open("GET", "/some/url?" + serObj, true); ajx.send();

Request method : POST ajx.open("POST", "/some/url", true);ajx.setRequestHeader("Content-Type",

"application/x-www-form-urlencoded");

ajx.send( serObj );

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Handle response

readyState property : request lifecycle 0 : uninitialized

1 : connection establised2 : request received3 : processing4 : finished

• onreadystatechange property

Successful response codes: 200 <= ajx.status < 300Not modified response : 304 (Safari : undefined)Every other codes will be considered error

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Update UI

Reading the Resulting Data

responseXML : This property will contain a reference to a precomputed DOM document

responseText : This property contains a reference to the raw text string of data returned

by the server

ajx.onreadystatechange = function(){ if ( ajx.readyState == 4) {

if (ajx.status >= 200 && ajx.status < 300) {var scores = document.getElementById("testDiv"); scores.innerText = ajx.responseText;

}}

};

Example

http://www.learn-ajax-tutorial.com/

Javascript Performance

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Some tips

DOM access : Interaction with the DOM is usually slower than normal JavaScript code

for-in loops : most JS environments have slow implementation

eval and Function constructor : avoid using because overhead is involved in script evaluation

//expensive operationsvar func = new Function(“alert('test')”);

Pass functions, not strings, to setTimeout() and setInterval()

http://wiki.forum.nokia.com/index.php/JavaScript_Performance_Best_Practices