What was actually handed to fetch — the request, as this session made it.
verb: string
Upper case, the way HTTP writes it and every log prints it.
url: string
Absolute, already resolved against the page.
headers: ReadonlyMap<string, string>
Lower-cased names, because HTTP says they are the same header either way.
body: string | null
null for the verbs that carry nothing, which is not the same as an empty body.