So you want to find out how many horizontal pixels you have available on a mobile device. This is super difficult because:
Many Bothan spies had to die for this code:
function effectiveDeviceWidth() {
var deviceWidth = window.orientation == 0 ? window.screen.width : window.screen.height;
// iOS returns available pixels, Android returns pixels / pixel ratio
// http://www.quirksmode.org/blog/archives/2012/07/more_about_devi.html
if (navigator.userAgent.indexOf('Android') >= 0 && window.devicePixelRatio) {
deviceWidth = deviceWidth / window.devicePixelRatio;
}
return deviceWidth;
}