java script security?

[hassan azizi]

hi i want to use java script files to store data in client computer like google's gmail mechanism for auto complete and speed matter. but i don't know how i can hide this file(which containes user data) from hackers just like gmail(i can't find gmail data in my computer and i can't save gmail page correctly to see my data stored in some files!) how gmail does it? and how i can prevent jscript file saving request from user? i'm wating thanks