window.onresize = function() { setScreenClass(); }; 
window.onload = function() { setScreenClass(); }; 

function setScreenClass()
{
    var fmt = document.documentElement.clientWidth;
    var cls = 
        (fmt <= 350) ? 'narrow' :
        (fmt > 350 && fmt <= 700) ? 'one' :
        (fmt > 700 && fmt <= 900) ? 'two' :
        (fmt > 900 && fmt <= 1100) ? 'three' :
        'wide';
        
    document.body.className = cls;
}