CODEWITHSUNDEEP
javascripthttpfetch-api
Piotr Zakrzewski
Piotr Zakrzewski

Reputation: 3891

HTTP request error code 429 cannot be caught

Using fetchApi I am issuing a POST request to an endpoint and catching errors like this:

fetch(new Request(url, {
  method: 'POST',
  headers: { ...defaultHeaders, ...headers } ,
  credentials: 'include',
  body: JSON.stringify(body)
})).then(
  // handle correct reponse
).catch(
  if (err.status === 401) {
       // handle error nicely
    } else if (err.status === 429) {
       // handle error differently
    } else {
      // handle error yet another way
    }
);

While 401 error is handled as expected, when the endpoint responds with 429 the code

else if (err.status === 429) {
       // handle error differently
    }

Is never executed.

EDIT1: the entire catch is never reached in case of 429

Are 401 and 429 status codes handled differently by javascript/browsers? How Can I catch 429 error and handle it my way?

Upvotes: 7

Views: 6605

Answers (1)

deceze
deceze

Reputation: 521995

Looks mostly like wrong expectations. The promise will only be rejected (and hence catch invoked) when the response's type is "error", which only seems to be the case for very specific, limited cases.

Per MDN, the fetch() API only rejects a promise when a “network error is encountered, although this usually means permissions issues or similar.” Basically fetch() will only reject a promise if the user is offline, or some unlikely networking error occurs, such a DNS lookup failure.

In other words, a request with a 429 response is still a successfully executed request.

The good is news is fetch provides a simple ok flag that indicates whether an HTTP response’s status code is in the successful range or not.

fetch("http://httpstat.us/500")
    .then(function(response) {
        if (!response.ok) {
            throw Error(response.statusText);
        }
    })

https://www.tjvantoll.com/2015/09/13/fetch-and-errors/

Upvotes: 10

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