Jquery to get set read access IFrame content TextBox Value Data

As you know that this days smart developers doesn't use IFRAME. But in our job always developers need to handle legacy systems. I found such type of legacy application. Now i am trying to modify the user requirement. To do that i need to read or access IFrame content as well as get or put some data from parent page to IFRAME. Since i did it thats why i want to share with you how one can access/