Different viewport for iPhone and iPad

gistfile1.js

var width = screen.width;
if (width >= 900) {
	$('meta[name=viewport]').attr('content','width=device-width, initial-scale=1');
} else if (width < 900 && width >= 700) { // iPad in portrait mode
	$('meta[name=viewport]').attr('content','width=device-width, initial-scale=0.8');
} else if (width <700) { // anything smaller than 700px in width 
	$('meta[name=viewport]').attr('content','width=device-width, initial-scale=0.4');
}