Getting API response payload using fetch

Question

I am using fetch to get the API response for GET and POST requests. When an error occurs, I am able to see the status code and the text i.e, 400 Bad Request. However, there is additional information being passed that explains why the error was thrown (i.e. username did not match). I can see this additional message in the response payload via Firefox developer tool's console but I am not sure how to get it via handling the fetch response.

Here's an example request:

fetch(url, {
  method: 'POST',
  body: JSON.stringify({
    name: name,
    description: description
  }),
  headers: {
    "Content-type": "application/json; charset=UTF-8",
    "Authorization": "Bearer " + token
  }
}).then(response => {
  if (!response.ok) {
    throw Error(response.statusText)

  }
  return response
})
.catch(error => {
  console.log(error)
})

Any ideas?

Answer 1

Thank you everyone for your suggestions.

This tutorial helped me understand what to do.

https://css-tricks.com/using-fetch/

My problem was that when there is an error, the response is not JSON, it's text. So I needed to do something like this (taken from css-tricks.com):

fetch('https://api.github.com/users/chriscoyier/repos')
.then(response => response.text())
  .then(data => {
    console.log(data)
  });

Answer 2

You seem to be passing only the statusText field of the response, which corresponds to the HTTP status code (And not the response body) - for example Bad Request for HTTP response code 400.

You can read the response body using one of the methods defined on the Response object returned by the fetch API. For example, if you're expecting a JSON response body, you can have:

const onSuccess = response => {
  // Do something with the response
  // What you return from here will go to the next .then
}

const onFailure = response => {
  // response.json() returns a promise that resolves to the JSON sent in the body
  // Note that whatever is returned from here will go to the next .then
  // To go to the next .catch, you can throw from here
  return response.json().then(jsonResponse => console.log(jsonResponse))
}

fetch(url, {
  method: 'POST',
  body: JSON.stringify({
    name: name,
    description: description
  }),
  headers: {
    "Content-type": "application/json; charset=UTF-8",
    "Authorization": "Bearer " + token
  }
}).then(response => {
  if (!response.ok) {
    throw response
  }
  return response
})
.then(onSuccess, onFailure)
.catch(err => { /* Any error thrown from the handlers will be caught here */ })

You can have a look at the Response object documentation for more details.

Answer 3

Based off the docs, I'd do something more along the lines of this:

const response = await fetch('http://example.com/movies.json')
const myJson = await response.json();
console.log(JSON.stringify(myJson));

Otherwise you have to do everything inside of your .then().

In regards to the additional text you are looking for, that's totally dependent on the response object, and I have no way of knowing without seeing it.

Answer 4

@Voxum, your answer is missing important info, like a method..and ; await is good, but remember it should be in an async function, and you dont need to use it if you "thenify" .then() as that returns the promise. from the Fetch docs, that is their basic get/HTML example. i think the OP is asking for a API call for different types of methods, which will require a more advanced setup.

The thing is with a 400 response, the server is not giving you a response message as the 404 (for example) is telling you the page is not found. Usually the only time a server will give you a response message is when you get a good (success/200). there will usually be a message at response.json() or response.text() depending on your data coming back.

after you call fetch with the url, method and any headers use .then((response) => {console.log(response.json());}); for json and use .then((response) => {console.log(response.text());}); for xml/text

OP has the fetch set up properly but just needs to use response.json() or response.text(). again, a 200 response can still be a "incorrect password" and this is where you'll use this. don't expect a response body on the 400/500s. good luck!