> It looks like they are just testing if objects can be transferrable. That's what I'd like to do with chunks, when possible.

Yes, you should test for that as well. But fallback here is not to not use worker if it fails, but to serialize chunks (which means a lot of copying). But it is still better to compute SHA in worker because it does not block UI.

> I think createObjectURL is not needed. We can just send chunk - it should be serializable. And we always have fallback in main thread.

Maybe you are right. Passing array directly probably does not copy it. But serialization does. But you are probably right that those browsers which do not support passing array directly probably do not support `createObjectURL` as well.