here is a previous thread on getting SIFT and the FLANN-based matcher to build for javascript:
It links to this issue, where someone explains what’s needed to make FLANN available. To me it sounds as if the procedure needs little adaptation to work for SIFT:
Perhaps try to include more than just the create method.
When in doubt, you could add a post to the other thread, directly pinging the relevant user by typing an @ and then their name. After typing the @, autocompletion should pop up.