simply countdown target update

[smogsy]

i have a text field named : countdown_time & a Set button named called: Set

i basically want user to type in there next Target Countdown Date in the text field and once clicked set the countdown set to the new countdown target.

i have added the function and it created this, as im still learning i would like some help in getting this to work. i think i need to change the ones bolded but i cannot seem to get it to work, thanks a lot.

function setNextCountdownTarget()
{
updateCurrentTime();

var nextEvent;
if (iCalendar != null) {
nextEvent = iCalendar[0].nextEvent();
}

if (nextEvent != null) {
setCountdownTarget({ eventTime: nextEvent.nextOccurrence, eventLabel: nextEvent.summary });
isTargetReached = false;
}
}

[smogsy]

no one can help?