Javascript : Detect the source of an event

Hi

I would like my function to detect the source of the event (onFocus vs onBlur) as in the sample script below.
Is it possible ?

I just spent more than an hour in the Acrobat JS documentation, I did not find anything and I have itchy eyes ...

myFunction() {
if (event is onFocus) {// blablabla;}
else if (event is onBlur) {// blebleble;}
}

Thank you