CODEWITHSUNDEEP
javascriptreactjserror-handlingfetch-api
Merim
Merim

Reputation: 1363

Fetch API error handling

I want to display error message from my API, problem is that I can't reach that error if I check for response.ok, it returns Fetch error, not the one from API..

If I don't use if(response.ok)... it returns the error from API but it dispatches the success action.

Here is the example, login action:

export const signIn = data => dispatch => {
  dispatch({ 
    type: SIGN_IN
    }) 
  fetch(API_URL+'/login', { 
   method: 'POST',
   headers: {
      'content-type': 'application/json'
      },
   body: JSON.stringify(data),
    })
    .then( response => {
    if (!response.ok) { throw response }
    return response.json()  //we only get here if there is no error
  })
  .then( json => {
    dispatch({
      type: SIGN_IN_SUCCESS, payload: json
    }),
    localStorage.setItem("token", 'Bearer '+json.token)
    localStorage.setItem("user", JSON.stringify(json.user))
  })
  .catch( err => {
    dispatch({
      type: SIGN_IN_FAILED, payload: err
    })
  })
    
}

This is the code for action that dispatches the right message but as success action, not as failed one..

export const signIn = data => dispatch => {
  dispatch({ 
    type: SIGN_IN
    }) 
  fetch(API_URL+'/login', { 
   method: 'POST',
   headers: {
      'content-type': 'application/json'
      },
   body: JSON.stringify(data),
    })
    .then( response => response.json())
  .then( json => {
    dispatch({
      type: SIGN_IN_SUCCESS, payload: json
    }),
    localStorage.setItem("token", 'Bearer '+json.token)
    localStorage.setItem("user", JSON.stringify(json.user))
  })
  .catch( err => {
    dispatch({
      type: SIGN_IN_FAILED, payload: err
    })
  })
    
}

Upvotes: 28

Views: 79022

Answers (3)

Sazzadur Rahman
Sazzadur Rahman

Reputation: 2930

With the following solution one can handle JSON API error, Generic API error and Generic fetch error

fetch("api/v1/demo", {
    method: "POST",
    headers: {
        "Content-Type": "application/json"
    },
    body: JSON.stringify({
        "data": "demo"
    })
})
    .then(response => {
        if (!response.ok) {
            return Promise.reject(response);
        }
        return response.json();
    })
    .then(data => {
        console.log("Success");
        console.log(data);
    })
    .catch(error => {
        if (typeof error.json === "function") {
            error.json().then(jsonError => {
                console.log("Json error from API");
                console.log(jsonError);
            }).catch(genericError => {
                console.log("Generic error from API");
                console.log(error.statusText);
            });
        } else {
            console.log("Fetch error");
            console.log(error);
        }
    });

Upvotes: 35

Amir Mohammad Moradi
Amir Mohammad Moradi

Reputation: 887

according to This Article :

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.

then, you can use this part of code to use non-network error handlings and make your code more readable

function handleErrors(response) {
    if (!response.ok) throw new Error(response.status);
    return response;
}

fetch("API URL")
    // handle network err/success
    .then(handleErrors)
    // use response of network on fetch Promise resolve
    .then(response => console.log("ok") )
    // handle fetch Promise error
    .catch(error => console.log(error) );

Upvotes: 20

Andreas Gelever
Andreas Gelever

Reputation: 2006

In order to extract API message from server in case of some error, you have to use the following idiom (which doesn't lie on the surface though), see link

     fetch("http://localhost:8090/test/error", {
        method: 'GET',
        headers: {
            'Accept': 'application/json'
        }
    })
        .then(result => {
            //Here body is not ready yet, throw promise
            if (!result.ok) throw result;
            return result.json();
        })
        .then(result => {
            //Successful request processing
            console.log(result);
        }).catch(error => {
            //Here is still promise
            console.log(error);
            error.json().then((body) => {
                //Here is already the payload from API
                console.log(body);
            });
        })

Verbose - yes!, but does exactly what is needed.

Upvotes: 19

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