How to check the date in this format dd/mm/yyyy is not less than current date and show app allert if the date is less than current?

Hello,

how to check the date in this format dd/mm/yyyy  in one field in adobe form is not less than current date and show app allert if the date is less than current?

I read this:
How to compare dates in Java? - Stack Overflow

But how can I use it in adobe pdf forms to check the start date is equal to  today date, if  it is less than today date then show me appalert message.

I tried this:

today.date = new Date();

var sStart = getField("fill_9").valueAsString;

dStart = util.scand("dd/mm/yyyy", sStart);

if ( new Date() < dStart) 

{

app.alert ( " alert"); 

} 

but it doesn't work.