Given are these strings:

var string1 = "Chapter_1";
var string2 = "Chapter_1a";

The desired result is:

"Chapter 1."
"Chapter 1. a)"

I could to this:

var string1new = string1.replace("_", " ").replace(/(d+)/, "$1.").replace(/.(w)$/, ". $1)"));
var string2new = string2.replace("_", " ").replace(/(d+)/, "$1.").replace(/.(w)$/, ". $1)"));

But I would prefer one single pattern/replacement. Something like:

var string1new = string1.replace("/(Chapter)_(d+)(w*)/", "$1 $2. $3)");
var string1new = string1.replace("/(Chapter)_(d+)(w*)/", "$1 $2. $3)");

Now how to conditionally insert $3) depending on whether $3 is empty or not?