Seen here.
function AddToCalendar(calendar,server,eid,date){ var url=server+'/calendar.ics?eid='+eid+'&calendar='+calendar; if(date) { url+='&date='+date; } else { if(document.mgform&&document.mgform.selecteddate) { if(document.mgform.selecteddate.selectedIndex<1) { alert('Please select the date you would like to attend.');return; } else { url+='&date='+document.mgform.selecteddate[document.mgform.selecteddate.selectedIndex].value;} } } if (calendar=='outlook'||calendar=='ical') document.location.href=url; else window.open(url,'calendar','toolbar=yes, menubar=yes, location=yes, status=yes, scrollbars=yes,resizable=yes, width=800, height=600, left=0, top=0'); }
and
<a href="javascript:AddToCalendar('google',%20'http://www.eventbrite.com',%20'547456457',%20'');">link</a>