How To Extend An Existing Custom Element?

I have a custom element, called x-foo. I would like to extend it, and create an x-foo-extended element, but it doesn't works. I get this error: Uncaught NotSupportedError: Failed t

Solution 1:

According to the spec , this is not permitted. From the spec: "If BASE does not exist or is an interface for a custom element, set ERROR to InvalidName and stop."

Source: As described by the person who implemented custom elements in Chrome https://lists.w3.org/Archives/Public/public-webapps/2014OctDec/0155.html