Javascript Basics Part III

Collections

• An object is an unordered collection of name/value pairs
• Names are strings
• Values are any type, including other objects
• Every object is a little database

Object Literals

• Object literals are wrapped in {}
• Values can be expressions
• : separate names and values
• , separates pairs
• Can be used anywhere value is required
• New members can be added to any object by simple assignment myObject[name]=value

Maker function

function maker(name, where)
{
	var it={};
	it.name=name;
	it.where=where;
	return it;
}

myObject = maker("Madhur Ahuja", "Jail");

Linkage

• Objects can be created with a secret link to another object
• The object(o) function will be used with a secret link to object o
• The linkage cannot be changed once created. It is possible in Mozilla implementation, but is non-standard.

var myNewObject = object (myOldObject);

• All objects are linked to Object.prototype
• All objects inherit some methods, none of them are useful
• Objects doesn’t have copy or equals methods. Omission from the language.

Object construction##

1. new Object()
2. {}
3. object(Object.protype)

• Second is the most preferred

• Objects are passed by reference

• === or == compares references not values

• members can be removed by using delete operator

Arrays

• Inherits from object
• No need to provide a length or type when creating array
• Have a special length member
• Array literal uses []
• myList = ['Oats' , 'peas']
• New items can be added myList[myList.length]='barley'
• The dot notation cannot be used. Should use subscript notation
• Methods: concat, join, pop, push, slice, sort , splice
• delete array[number] Removes the element, but leaves the hole
• array.splice(number, 1) Removes the element and renumbers all the following elements
• Use objects when names are arbitrary strings
• Use arrays when names are sequential integers