I have published the blog post
$1. I am sharing it here in the hopes that the members of the community will find it to be useful.
For those who wish to skip to the solution instead of reading the blog post, the following example explains how to specify a default value for optional parameters in a JAWS script function.
string function GetFavoriteNumberMessage(optional int number)
if (GetVariantType(number) == VT_EMPTY)
number = 42
endIf
var string message = FormatString("Hello. My favorite number is %1. What is your favorite number?", number)
return message
endFunction