How can I pass JSON body of Fetch response to Throw Error() with then()?

Question

EDIT: You've misunderstood. Consider this psuedo code. This is essentially what I want to do but it doesn't work when wrote like that.

Once you receive a Laravel 422 response with Fetch, the response doesn't contain the actual JSON data. You have to use response => response.json() to access it. I've put a picture of what the responseholds and I've also supplied the output after using response => response.json().

I am NOT trying to convert an object into a JSON string.

I'm using SweetAlert2 with Laravel.

throw error(response => response.json())

swal({
  title: 'Are you sure you want to add this resource?',
  type: 'warning',
  showCancelButton: true,
  confirmButtonText: 'Submit',
  showLoaderOnConfirm: true,
  allowOutsideClick: () => !swal.isLoading(),
  preConfirm: () => {
    return fetch("/resource/add", {
        method: "POST",
        body: JSON.stringify(data),
        credentials: "same-origin",
        headers: new Headers({
          'X-CSRF-TOKEN': $('meta[name="csrf-token"]').attr('content'),
          'Content-Type': 'application/json',
          'Accept': 'application/json'
        })
      })
      .then(response => {
        if (!response.ok) {

          // How can I return the response => response.json() as an error?
          // response.json() is undefined here when used

          // throw Error( response => response.json() ); is what I want to do
          throw Error(response.statusText);

        }
        return response;
      })
      .then(response => response.json())
      .then(res => console.log('res is', res))
      .catch(error => console.log('error is', error));
  }
})

response holds the following after response => response.json() and it's this JSON that I want to pass to error().

{"message":"The given data was invalid.","errors":{"name":["The name field is required."],"abbrev":["The abbrev field is required."]}}

I make an AJAX call and if Laravel's validation fails, it returns a status 422 with the validation error messages in JSON. However, Fetch doesn't count 422 responses as an 'error' so I have to manually trigger it myself with throw.

Because my validation messages are in the JSON response i.e. then(response => json()) how can I convert my response to json and then pass it to my throw error() ?

Just FYI, this is what console.log(response) holds before using response => response.json()

Answer 1

Something like this should work:

fetch(...)
  .then((response) => {
    return response.json()
      .then((json) => {
        if (response.ok) {
          return Promise.resolve(json)
        }
        return Promise.reject(json)
      })
  })