java script code

hello,
i wants to design and develop a exactly same from of following link:-

http://www.magicbricks.com/post-property-for-sale-rent/residential-commercial

but i am facing some problem to identify what is the type of java script is working to hide the fields and displays some other fields on selection of drop down list.
please tell me how can i design and develop a new working form exactly like above link's from as soon as possible.
thank you.