a submillisecond version of Date.now() based on based on window.performance.now()

submsNow.js

/**
 * precise version of Date.now() -
 * It provide submillisecond precision based on window.performance.now() when 
 * available, fall back on Date.now()
 * see http://updates.html5rocks.com/2012/05/requestAnimationFrame-API-now-with-sub-millisecond-precision 
*/
var nowSubms	= (function(){
	var p	= window.performance	|| {};
	if( p.now )		return function(){ return p.timing.navigationStart + p.now();		};
	else if( p.mozNow )	return function(){ return p.timing.navigationStart + p.mozNow();	};
	else if( p.webkitNow )	return function(){ return p.timing.navigationStart + p.webkitNow()	};
	else if( p.mskitNow )	return function(){ return p.timing.navigationStart + p.msNow()		};
	else if( p.okitNow )	return function(){ return p.timing.navigationStart + p.oNow()		};
	else			return function(){ return Date.now();					};	
})();