While checking the conditions, if the monitor resolution is 1024×768 it should call one functions, and if monitor resolution will change to 1280×1024 shuuld call some other function,
That is about the only use for screen resolution as for everything else you only get to work with the space in the window and all the screen resolution tells you about that is that it will definitely be smaller.
If you are using the size for anything other than opening a new window you need to test the browser window size and how you do that is different for different browsers. See http://javascript.about.com/library/blscreen2.htm for a copy of the functions that I wrote that can retrieve that info by using whichever method the browser supports.