The current definitions of createAnswer and createOffer of RTCPeerConnection don't match the functions defined in the W3C specification.
createAnswer(successCallback?: RTCSessionDescriptionCallback, failureCallback?: RTCPeerConnectionErrorCallback): Promise<RTCSessionDescription>;
createOffer(successCallback?: RTCSessionDescriptionCallback, failureCallback?: RTCPeerConnectionErrorCallback, options?: RTCOfferOptions): Promise<RTCSessionDescription>;
W3C interface specification:
Promise<RTCSessionDescriptionInit> createOffer(optional RTCOfferOptions options);
Promise<RTCSessionDescriptionInit> createAnswer(optional RTCAnswerOptions options);
W3C legacy interface extensions:
Promise<void> createOffer(RTCSessionDescriptionCallback successCallback, RTCPeerConnectionErrorCallback failureCallback, optional RTCOfferOptions options);
Promise<void> createAnswer(RTCSessionDescriptionCallback successCallback, RTCPeerConnectionErrorCallback failureCallback);