Script to make texts bold or italic

I saw someone suggested the following code to meet the need:

var app = new Illustrator.Application();

var doc = app.ActiveDocument;

var bold = doc.CharacterStyles["Bold"];

var italic = doc.CharacterStyles["Italics"];

var frame = doc.TextFrames[0];

bold.ApplyTo(frame);

italic.ApplyTo(frame);

But it does work in my case since "doc.CharacterStyles["Bold"];" and "doc.CharacterStyles["Italics"]" declare an error message of "No such element". Is there another way that I can try to make texts bold or italic?