You can only call res.json() on a response once.

const res = await fetch(…)
await res.json() // works
await res.json() // doesn’t work

.json (or .text, .arrayBuffer, .formData, etc) consumes the body. Once the body has been consumed it cannot be consumed again.

Same for request objects if you are using route handlers. req.json() can only be called once.

@joulev I get that. My problem is that someone is eating my responses, and I don't know who. i.e. our app has two very standardised functions that call fetch and then transform that to a typed response object. Neither of them have an execution path that would call .json() twice. So it must be something "in the stack" - looking for hints on what that may be.

Interesting, could you send an example?

fwiw, you can res.clone().json() tho :)
-# assuming you clone before you consume body