JScript / JavaScript Extension Feature

From: http://amix.dk/blog/viewEntry/19360

function addToDate ( date , hours , minutes ) { 
var m_secs = date . getTime (); 
var local_offset = date . getTimezoneOffset () * 60 * 1000 ; 
var utc_m_secs = m_secs + local_offset ; 

	if ( hours ) 
		utc_m_secs += hours * 60 * 60 * 1000 ; 
	if ( minutes ) 
		utc_m_secs += minutes * 60 * 1000 ; 
	return new Date ( utc_m_secs ); 
	} 

Example: var four_hours_ago = addToDate ( new Date () , -4 );