Duplicate a track without media or automation, renaming it to remove ".dup" and add a number

Nice. Also try this version. It will use a lowercase letter if your original letter was also lowercase.

sf.ui.proTools.selectedTrack.trackRename({
    renameFunction: function (name) {
        var letters = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'];

        //This function gets called after the Rename track dialog is open
        //the argument 'name' holds the existing name, eg. "Audio B.dup1"
        //We're supposed to eventually return the target name we want from this function.

        var grps = name.match(/^(.*)([ \d])([a-zA-Z])(\.dup.*|)$/);
        //This regular expression matches a string containing of the following groups (each group is in parentheses)
        //Group 1 - syntax: (.*) - meaning: Match any number (*) of any characters (.) This will match "Audio"
        //Group 2 - syntax: ( ) - meaning: Match 1 space character 
        //Group 3 - syntax: ([a-zA-Z])  - meaning: Match 1 character that is a letter. This will match "B"
        //After last group- syntax: \.dup.* - meaning: Match a dot (\.), the text "dup", and then ANY character (.), any number of times (*)

        //Save out the groups, baseName, space, numName
        var baseName, space, numName;
        if (grps) {
            baseName = grps[1];
            space = grps[2];
            numName = grps[3];
        } else {
            //It didn't match our format. Try again without the requirement of a suffix
            if (name.indexOf('.dup') >= 0)
                baseName = name.substring(0, name.indexOf('.dup')); //Get the base name before any .dup
            else
                baseName = name;
            space = " "; //default space
            numName = "";
        }

        //If you didn't have a number, by default we want a space ' ' before our new #2 track
        if (numName == "") space = " ";

        //Create the new number. If there wasn't one, we'll default to 2, if there was one, convert our string to a number, and add 1 to that
        var newIndex = 1; //Start with 2nd index (1 because indices are always 0-based)
        if (numName) {
            var idx = letters.indexOf(numName.toUpperCase()); //Find the index (0-based)
            if (idx >= 0) {
                newIndex = idx + 1; //Set to the found index + 1
            }
            //If not found, default to 2nd index (1) which is already set
        }
        if (newIndex < 0 || newIndex >= letters.length)
            throw 'New index out of bounds'; //We reached Z or some other error

        var letter = letters[newIndex];
        if (numName && numName.toLowerCase() === numName)
            letter = letter.toLowerCase(); //Make letter lowercase if the input was lowercase

        //Return the new name, a combination of the base name "Audio", a space or not " ", and the new letter
        return baseName + space + letter;
    }
});