In the new Yahoo mail inbox, when u click the message it is displayed in a tab automatically (I guess with out server interaction). Does that mean Yahoo loads all the data first and then use them with java script when requested or not...anyho i don't have any idea and I would like if some one explain to me how it works since am planning to do the same with my application. I am sure this will boost application performance and i am eager to know.
I have not seen it but what you're describing sounds like dynamic AJAX loading. Basically, only load information when it is requested by the user. This will reduce network load and initial loading times. Most JS libraries have some form of AJAX helper. You can read more on AJAX here and here.