I would like to make a web application with a “responsive design” to post back to the server the JavaScript screen resolution and make decisions based on that information, but the question is can I rely on window.screen to always supply the correct laptop, tablet, smartphone information?
And of course taking into consideration that it support only modern browsers and devices.
Yes,
screen.widthandscreen.heightare reliable, however you probably would be more interested in the size of the window for laying out your pages. For instance,@mediaqueries in CSS3 use the window size, not the screen size.