Add a currency comma in a PDF when format is already used to display an “event.value” in a text field

I’m a real novice when it comes to Javascript and the issue I’m having is a text field in a PDF form already has a custom format to add the text “Check Amount”, which disappears when typing in the text field. The struggle is having it add a comma(s) for currency and the number format won’t allow the displayed text at the same time. Below is the custom format javascript being used:

if (!event.value) { 
event.value = "Check Amount";
event.target.display = display.noPrint;
} else {
event.target.display = display.visible;
}

How do I add a currency format to it?

I’ve seen this javascript by KHKonsulting LLC, but the prefilled text of “Check Amount” disappears completely:

var f = this.getField("SomeField");
f.setAction("Format", "AFNumber_Format(2, 0, 0, 0, "", true);");
f.setAction("Keystroke", "AFNumber_Keystroke(2, 0, 0, 0, "", true);");