i am not sure i understand. if no options.frame is passed and there is no more frame with iddefault in n-vue frame cache (because there are actually 2 frames with iddefault and one was removed) then there is no fallback toFrame.topmost()?

getFrame(id) returns a frame from the frameMap - which is set/unset in the<Frame> componentmounted/destroyed callbacks.

So when we destroy the 2nddefault frame it's unset from theMap - but then$navigateTo is called, and by default theframe option is set todefault, so it ends up usingFrame.getFrameById('default') which returns the remainingFrame<default> that we pass as a fallback togetFrame(id, fallback) -> which then adds it back to the frameMap and returns it's vue VM instance... Essentially restoring it's entry to the frameMap.

It's a bit weird how we handle this, and the reason we even have the frameMap is because core will only return the frame fromgetFrameById if it has been navigated at least once... Perhaps it would make sense to patch that in core at some point and then refactor this whole setup to not rely on the frameMap.

@rigor789 thanks for the explanation. I get it now! seems good to me