objects, collections, linkage, invocations, this, typeof, closure, namespace, inheritance

Objects

–-Everything else is objects

–-Objects can contain data and methods

–-Objects can inherit from other objects.

 

•Collections

–-An object is an unordered collection of name/value pairs

–-Names are strings

–-Values are any type, including other objects

–-Good for representing records and trees

–-Every object is a little database

§var FUNC = function () {

§ var objDiv = document.createElement("div");

§ this.getCollection = function ( collection ) {

§ for ( i in collection ) {

§ objDiv.innerHTML += "name : " + i + "<br>value : " + collection[i] + "<br>";

§ }

§ document.body.appendChild(objDiv);

§ }

§}

§FUNC = new FUNC();

 

•Object Literals

–-Object literals are wrapped in { }

–-Names can be names or strings

–-Values can be expressions

–-: separates names and values

–-, separates pairs

–-Object literals can be used anywhere a value can appear

 

•Linkage

–-Objects can be created with a secret link to another object.

–-If an attempt to access a name fails, the secret linked object will be used.

–-The secret link is not used when storing. New members are only added to the primary object.

–-The object(o) function makes a new empty object with a link to object o.

function object(o) {

function F() {};

F.prototype = o;

return new F();

}

 

•JavaScript Invocations

–-If a function is called with too many arguments, the extra arguments are ignored.

–-If a function is called with too few arguments, the missing values will be undefined.

–-There is no implicit type checking on the arguments.

–-There are four ways to call a function:

§Function form

–functionObject(arguments)

§Method form

–thisObject.methodName(arguments)

–thisObject["methodName"](arguments)

§Constructor form

–new functionObject(arguments)

§Apply form

–functionObject.apply(thisObject, [arguments])

 

•JavaScript this

–-this is an extra parameter. Its value depends on the calling form.

–-this gives methods access to their objects.

–-this is bound at invocation time.

Invocation form	this
function	the global object
method	the object
constructor	the new object

 

JavaScript typeof

type	typeof
object	'object'
function	'function'
array	'object'
number	'number'
string	'string'
boolean	'boolean'
null	'object'
undefined	'undefined'

 

•Closure

–-The scope that an inner function enjoys continues even after the parent functions have returned.

–-This is called closure.

§function getClosure () {

§  var num = 1;

§  var getAlert = function() { num++; alert(num); }

§  num++;

§  return getAlert();

§}

§<input type="button" value="getClosure" onclick="getClosure();">

 

–function fade(id) {

–    var dom = document.getElementById(id),

–        level = 1;

–    function step () {

–        var h = level.toString(16);

–        dom.style.backgroundColor =

–            '#FFFF' + h + h;

–        if (level < 15) {

–            level += 1;

–            setTimeout(step, 100);

–        }

–    }

–    setTimeout(step, 100);

–}

 

•JavaScript Namespace

–-Every object is a separate namespace.

–-Use an object to organize your variables and functions.

–-The YAHOO Object.

§var YAHOO = {};

§YAHOO.url = "http://www.yahoo.com";

§YAHOO.getUrl = function () {

§ alert(this.url);

§ return this.url;

§}

§<input type="button" value="YAHOO.getUrl();" onclick="YAHOO.getUrl();">

 

•Inheritance

–-Linkage provides simple inheritance.

–-Prototypal inheritance.

–-Parasitic inheritance.

–-Method apply(), call().

 

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