how to fit "frame to content" for a selected textframe by user?

hi

i am creating a script in which a textframe is selected and several operations are performed but on a line i got stuck since morning.

var sourceDoc = app.activeDocument;

var myFrame = sourceDoc.selection;

myFrame.fit(FitOptions.FRAME_TO_CONTENTS); // error here myFrame.fit is not a function

I tried with

app.activeDocument.selection.fit(FitOptions.FRAME_TO_CONTENTS); // error again

then i copied that textframe to new document and tried.

app.activeDocument.pageItems[0].fit(FitOptions.FRAME_TO_CONTENTS); /// it works fine

Please help.

thanks

virender