Change fontStyle

Hello,

I am trying to change the style of a font through a script.
I manage to change the Font itself like this:

var textProp = app.project.activeItem.layer(1);
var textDocument = textProp.value;
textDocument.font = "Arial";
textProp.setValue(textDocument);

Unfortunately I don't manage to change the style;

I tried this way :

textDocument.fontStyle = "Bold";

ial";

But it seems that the fontStyle is in Read Only.

Do you need if it's possible to by-pass this issue.

Thanks by advance,

Aurélien