I hope you are doing this on a mobile device eydg, because the width of your screen, ie; your monitor, does not change. My screen is 1440 px wide so this does work on my screen:
if(screen.width <= 1440) $('.bigga').hide();
And your code should work if your checking it on a suitable device. Maybe you should use the size of 320 instead of 240.
A good place to look maybe https://developer.mozilla.org/en-US/.../Media_queries
and use css instead of jquery.
If you are not working with a cell or a tablet you need to use the width of the browser.