I want to make "mono to stereo"

Hello Gurus.

I want to make "mono to stereo" script.

It turns two mono tracks into a single stereo track.

It looks like this image.

For that I created a script.

//store selection target track
var originallySelectedTrackNames = sf.ui.proTools.selectedTrackNames.slice();

//copy target clip
sf.ui.proTools.menuClick({
    menuPath: ["Edit","Select All"],
});

sf.ui.proTools.menuClick({
    menuPath: ["Edit","Copy"],
});

//make new stereo track
sf.ui.proTools.menuClick({
    menuPath: ["Track","New..."],
});

sf.ui.proTools.windows.whoseTitle.is("New Tracks").first.elementWaitFor();

sf.ui.proTools.windows.whoseTitle.is("New Tracks").first.popupButtons.whoseDescription.is("Track format").first.popupMenuSelect({
    menuPath: ["Stereo"],
});

sf.ui.proTools.windows.whoseTitle.is("New Tracks").first.popupButtons.whoseDescription.is("Track type").first.popupMenuSelect({
    menuPath: ["Audio Track"],
});

sf.ui.proTools.windows.whoseTitle.is("New Tracks").first.textFields.whoseTitle.is("Track Name").first.elementSetTextFieldWithAreaValue({
    value: "stereo",
});

sf.ui.proTools.windows.whoseTitle.is("New Tracks").first.buttons.whoseTitle.is("Create").first.elementClick();

sf.ui.proTools.windows.whoseTitle.is("New Tracks").first.elementWaitFor({
    waitType: "Disappear",
});

sf.ui.proTools.invalidate().trackSelectByName({ names: originallySelectedTrackNames });


sf.keyboard.press({
    keys: "semicolon",
});



//paste clip
sf.ui.proTools.menuClick({
    menuPath: ["Edit","Paste"],
});


//Hide original track
sf.ui.proTools.invalidate().trackSelectByName({ names: originallySelectedTrackNames });

sf.ui.proTools.selectedTrack.titleButton.popupMenuSelect({
    menuPath: ['Hide and Make Inactive'],
    isRightClick: true,
});

However, in my inexperience, I could only name the finished track "stereo".
The rule making I want to do is
1.Extract the common string from the track names of the two selected tracks.
(If this is all you have, for example, "pf.L" and "pf.R" it will end up with "pf.")
2.So, Erase the last letter. Or erase the last character if it is a symbol.

Please let me know how to do this.

Thank you.

Yujiro