MDN URL: https://developer.mozilla.org/en-US/docs/Web/API/Response/json

What information was incorrect, unhelpful, or incomplete?

This function can raise exceptions, but these are not documented. Try using it on a response that is not actually JSON, e.g.

Specific section or headline?

Exceptions

What did you expect to see?

The list of possible exceptions and their causes. See the fetch documentation for an example of a function that documents its exceptions well.