Customer fillable field populate data into new field

[rickwtexas]

For those that do forms all the time, I'm sure this is super simple. I have a small window to create/design 26 fillable pdf spec sheets, and all need to be able to do the following:

Customer enters an option code in Category 1, then Category 2, the Category 3, and the data popluates into a order # in a field below with a "–" seperating each code. 

I've done this before but it was 8 or 9 years ago and I've barely slept since then I tried to cobble the Java together but it does nothing. Help is seriously appreciated. Sorry if I have the wording wrong, I only do forms once a decade... (if there was book on pdf form creation I'd buy it). 

[try67 · Accepted solution]

Try this:

var s1 = this.getField("Category1").valueAsString;
var s2 = this.getField("Category2").valueAsString;
var s3 = this.getField("Category3").valueAsString;
if (s1 && s2 && s3)
	event.value = s1+"-"+s2+"-"+s3;
else event.value = "";

[rickwtexas]

Thanks! Saved my buttocks.