Zoom website depending on monitor width?

I'm looking for a javascript to change the zoom of the website depending on the viwewers screen resolution. I made the website on my desktop with 1920x1080p :/

html { -moz-transform: scale(0.75, 0.75); zoom: 0.75; zoom: 75%; }

I got this in my css to zoom the website to my liking for MacBook (1280 x 800).

However I have no idea how to enable/disable it using javascript (if its possible?) and how to detect the resolution.