onResolve doesn't trigger if response is empty

Hello,

Thanks for the library 😃

I’m looking at the useFetch hook and specifically the associated onResolve callback to make a call to my backend and redirect to another URL if the call is successful using this pattern:

let { ... } = useFetch(`${url}`, withAuth(meta, token), {
   defer: true,
   onResolve: data => {
     console.log("Just resolved", data);
     // Redirect will go here
   }
 });

I have absolutely no problem reaching my console.log if I return data in my response in my Express backend like so:

return res.json({
    status: "ok"
});

However, sending an empty 200 response like so:

return res.sendStatus(200);

never triggers the onResolve callback and the console.log is never printed.

Is this the intendend behavior ?

If it is, maybe editing the documentation and mentionning the required data in the response would be helpful.

I’m happy to have a look and PR if needed 😃

[ghengeveld]

We should change the automatic json deserialization to look at Content-Type instead of Accept. The former indicates what the server response contains, the latter indicates what kind of request body it accepts. Looking at the Accept header is a mistake.

Additionally, I would like to extend the json deserialization to error responses as well. Many servers return a json-encoded error message in the body for error responses, which currently is hard to retrieve with useFetch.

[phryneas]

As your withAuth returns the "Accept": "application/json" header, useFetch assumes that the response from the server is JSON and tries to parse it as JSON. But the server returns an empty response - that cannot be parsed as JSON by JavaScript.

Try running JSON.parse(""), you’ll get SyntaxError: JSON.parse: unexpected end of data at line 1 column 1 of the JSON data as error (slightly different behaviour in other browsers).

Either your server needs to return valid JSON or your headers should not indicate that the server should return JSON.

I’d say all of this is exactly expected behaviour: the server is returning invalid JSON although you specificly requested JSON from the server.