Can I detect Tor Browser inside the browser itself, via Javascript I suppose?

I'd like to disable some features of a web app I'm building, if the browser is Tor Browser. Can I inside the browser itself (client side, not server side) find out if the browser is Tor Browser?

Background: In my case, Tor Browser pops up a dialog that asks the user "Should Tor Browser allow this website to extract HTML5 canvas image data?", because, says Tor Browser, canvas image data can be used to uniquely identify a browser.