Javascript

Javascript is used to include code into a webpage.

It has elements of both object oriented(OO) and functional programming although not necessarily in a conventional way. In JavaScript, everything is an object, except for the primitive data types. We can support OO like features such as:

• inheritance: through the prototype keyword.
• encapsulation: we can provide access to an objects data using functions.

Syntax

function functionname(var1,var2,...,varX)
{
some code
}

functionname=function(){  
   return (2*3);  
 }

switch (expr) {
   case SOMEVALUE: 
     //statements;
     break;
   case ANOTHERVALUE: 
     //statements;
     break;
   default:
     //statements;
     break;
 }

Datatypes

Primitive data types:

• Undefined
• Null
• Boolean
• Number
• String

built-in objects

• Array,
• Image
• Date
• String
• Number
• Math

host objects

• window
• document
• forms

Object Oriented

We can create a single instance of an object either by:

• Create a function which does not return a value and methods are inner functions
• Or create an object and then extend it.

So we could start from a function which becomes the constructor function:

function Rectangle(width,height){  
 this.width = width;  
 this.height = height;  
 function getArea(){  
   return (this.width*this.height);  
 }  
}

Or we could do it this way:

Rectangle=Object();
Rectangle.width=10;
Rectangle.height=20;  
Rectangle.getArea=function(){  
   return (this.width*this.height);  
 }

Or we could use an object literal:

Rectangle={width:10,height:20}

We create new instances of this object by stamping out copies of it using the new keyword:

var myRectangle = new Rectangle(10,20);

Or we could modify the constructor function to become a class factory removing the need to create classes using new:

myRectangle=function(width,height){
 var temp={};
 temp.width = width;  
 temp.height = height;  
 temp.getArea=function(){  
   return (this.width*this.height);  
 }
 return temp;
}

We can the create new instances as follows:

myRectangle2=myRectangle(30,40)

Every function/object has some private variables automatically created to support object like features:

• argument - holds an array of the arguments passed to the function.
• prototype - In every object constructor to allow you to add properties/methods to all objects created from that object constructor.
• constructor - returns the function object that created that instance of the object.

EuclideanSpace

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