Using Constants

I have started to explore the use of Constants and although there are a couple of posts on here which have helped me, I seem to missing something somewhere.

I have a document open which is in Gray Gamma 2.2
Using the code below always returns false when I thought it would be true

What have I done wrong please

app.activeDocument.mode == constants.ColorModel.GRAYSCALE

I’m currently not in front of PS but I think it needs to be app.activeDocument.mode == constants.DocumentMode.GRAYSCALE