How to get Readable error response from JavaScript Fetch API? - javascript

I am working on Reactjs redux on front-end and Rails API as a back-end.
So now I call API with Fetch API method but the problem is I cannot get readable error message like what I got inside the network tabs
this is my function
export function create_user(user,userInfoParams={}) {
return function (dispatch) {
dispatch(update_user(user));
return fetch(deafaultUrl + '/v1/users/',
{
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json'
},
method: "POST",
body: JSON.stringify(userInfoParams)
})
.then(function(response) {
console.log(response);
console.log(response.body);
console.log(response.message);
console.log(response.errors);
console.log(response.json());
dispatch(update_errors(response));
if (response.status >= 400) {
throw new Error("Bad response from server");
}
})
.then(function(json){
console.log("succeed json re");
// We can dispatch many times!
// Here, we update the app state with the results of the API call.
dispatch(update_user(json));
});
}
}
But when errors came I cannot figure out how to get readable response message like I got when I check on my browser network tabs
So this is what I got from the network tabs when I got errors.
My console
This is my rails code
def create
user = User.new(user_params)
if user.save
#UserMailer.account_activation(user).deliver_now
render json: user, status: 201
else
render json: { errors: user.errors }, status: 422
end
end
But I cannot find out how can I get that inside my function

Since the text is hidden inside promise within response object, it needs to be handled like a promise to see it.
fetch(bla)
.then(res => {
if(!res.ok) {
return res.text().then(text => { throw new Error(text) })
}
else {
return res.json();
}
})
.catch(err => {
console.log('caught it!',err);
});

Similar to your answer, but with a bit more explanation... I first check if the response is ok, and then generate the error from the response.text() only for the cases that we have a successful response. Thus, network errors (which are not ok) would still generate their own error without being converted to text. Then those errors are caught in the downstream catch.
Here is my solution - I pulled the core fetch function into a wrapper function:
const fetchJSON = (...args) => {
return fetch(...args)
.then(res => {
if(res.ok) {
return res.json()
}
return res.text().then(text => {throw new Error(text)})
})
}
Then when I use it, I define how to handle my response and errors as needed at that time:
fetchJSON(url, options)
.then((json) => {
// do things with the response, like setting state:
this.setState({ something: json })
})
.catch(error => {
// do things with the error, like logging them:
console.error(error)
})

even though this is a bit old question I'm going to chime in.
In the comments above there was this answer:
const fetchJSON = (...args) => {
return fetch(...args)
.then(res => {
if(res.ok) {
return res.json()
}
return res.text().then(text => {throw new Error(text)})
})
}
Sure, you can use it, but there is one important thing to bare in mind. If you return json from the rest api looking as {error: 'Something went wrong'}, the code return res.text().then(text => {throw new Error(text)}) displayed above will certainly work, but the res.text() actually returns the string. Yeah, you guessed it! Not only will the string contain the value but also the key merged together! This leaves you with nothing but to separate it somehow. Yuck!
Therefore, I propose a different solution.
fetch(`backend.com/login`, {
method: 'POST',
body: JSON.stringify({ email, password })
})
.then(response => {
if (response.ok) return response.json();
return response.json().then(response => {throw new Error(response.error)})
})
.then(response => { ...someAdditional code })
.catch(error => reject(error.message))
So let's break the code, the first then in particular.
.then(response => {
if (response.ok) return response.json();
return response.json().then(response => {throw new Error(response.error)})
})
If the response is okay (i.e. the server returns 2xx response), it returns another promise response.json() which is processed subsequently in the next then block.
Otherwise, I will AGAIN invoke response.json() method, but will also provide it with its own then block of code. There I will throw a new error. In this case, the response in the brackets throw new Error(response.error) is a standard javascript object and therefore I'll take the error from it.
As you can see, there is also the catch block of code at the very end, where you process the newly thrown error. (error.message <-- the error is an object consisting of many fields such as name or message. I am not using name in this particular instance. You are bound to have this knowledge anyway)
Tadaaa! Hope it helps!
I've been looking around this problem and has come across this post so thought that my answer would benefit someone in the future.
Have a lovely day!
Marek

If you came to this question while trying to find the issue because response.json() throws "Unexpected token at position..." and you can't find the issue with the JSON, then you can try this, basically getting the text and then parsing it
fetch(URL)
.then(async (response) => {
if (!response.ok) {
const text = await response.text()
throw new Error(text)
}
// Here first we convert the body to text
const text = await response.text()
// You can add a console.log(text), to see the response
// Return the JSON
return JSON.parse(text)
})
.catch((error) => console.log('Error:', error))
.then((response) => console.log(response))

I think you need to do something like this
export function create_user(user,userInfoParams={}) {
return function (dispatch) {
dispatch(update_user(user));
return fetch(deafaultUrl + '/v1/users/',
{
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json'
},
method: "POST",
body: JSON.stringify(userInfoParams)
})
.then(function(response) {
console.log(response);
console.log(response.body);
console.log(response.message);
console.log(response.errors);
console.log(response.json());
return response.json();
})
.then(function(object){
if (object.errors) {
dispatch(update_errors(response));
throw new Error(object.errors);
} else {
console.log("succeed json re");
dispatch(update_user(json));
}
})
.catch(function(error){
this.setState({ error })
})
}
}

You can access the error message with this way:
return fetch(deafaultUrl + '/v1/users/',
{
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json'
},
method: "POST",
body: JSON.stringify(userInfoParams)
})
.then(function(response) {
console.log(response);
console.log(response.body);
console.log(response.message);
console.log(response.errors);
console.log(response.json());
dispatch(update_errors(response));
if (response.status >= 400) {
throw new Error("Bad response from server");
}
})
.then(function(json){
console.log("succeed json re");
// We can dispatch many times!
// Here, we update the app state with the results of the API call.
dispatch(update_user(json));
})
// here's the way to access the error message
.catch(function(error) {
console.log(error.response.data.message)
})
;

The best choice is not to catch the error in the fetch because this will be useless:
Just in your api put a response with not code error
static GetInvoicesAllData = async (req,res) =>
{
try{
let pool = await new Connection().GetConnection()
let invoiceRepository = new InvoiceRepository(pool);
let result = await invoiceRepository.GetInvoicesAllData();
res.json(result.recordset);
}catch(error){
res.send(error);
}
}
Then you just catch the error like this to show the message in front end.
fetch(process.env.REACT_APP_NodeAPI+'/Invoices/AllData')
.then(respuesta=>respuesta.json())
.then((datosRespuesta)=>{
if(datosRespuesta.originalError== undefined)
{
this.setState({datosCargados:true, facturas:datosRespuesta})
}
else{ alert("Error: " + datosRespuesta.originalError.info.message ) }
})
With this you will get what you want.

You variables coming back are not in response.body or response.message.
You need to check for the errors attribute on the response object.
if(response.errors) {
console.error(response.errors)
}
Check here https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch
You should actually be returning an error response code from the server and use the .catch() function of the fetch API

First you need to call json method on your response.
An example:
fetch(`${API_URL}`, {
method: 'post',
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json'
},
body: JSON.stringify(userInfoParams)
})
.then((response) => response.json())
.then((response) => console.log(response))
.catch((err) => {
console.log("error", err)
});
Let me know the console log if it didn't work for you.

Related

React/Javascript - TypeError: Cannot read properties of undefined (reading 'json')

React & Javascript noob here, I'm trying to build my first React project. What I want to do is to have a button that fetches automatically the last matches I played on a game. I'm using a API that, when called correctly, returns this json:
{data:
[{id: 0, internal_id: "_map_id_halo1_pillar_of_autumn", name: "The Pillar Of Autumn"},
…]}
I want to extract the name for each object of data and display an unordered list below the button.
But when I click the button, the browser displays the error:
TypeError: Cannot read properties of undefined (reading 'json')
The code that does what I mentioned is as follows:
async fetchHaloMaps()
{
const url = 'https://cryptum.halodotapi.com/games/hmcc/metadata/maps'
const mapNames = [];
fetch(url, {
"method": 'GET',
"headers": {
'Content-Type': 'application/json',
'Cryptum-API-Version': '2.3-alpha',
'Authorization': 'Cryptum-Token XXX'
}
})
.then(response => {
console.log(response);
if (!response.ok)
throw new Error("Response not ok!");
})
.then(response =>
response.json())
.then(data => {
const i=0;
for (const d of data)
{
mapNames[i] = d.name;
i++;
}
this.setState((state, props) => ({
numberOfMaps : i
}));
})
.catch(error => {
console.log("There was an error: " + error);
});
}
I think I'm "parsing" the JSON in the wrong way. But in the JSON, data i indeed an array with a "name" attribute. So I wanted to cycle the data array and copy the attribute "name", but the code above is not working.
I know the HTTP request with fetch does succeed, since in the console.log I can see the response object and it has the 200 OK field, and I can see the JSON associated with the browser developer tools.
You did not return anything from this .then:
.then(response => {
console.log(response);
if (!response.ok)
throw new Error("Response not ok!");
})
so there is no value that gets passed along to the next .then.
While you could do return response, a better approach would be to remove the intermediate .then entirely - only insert a .then when you need to wait for something asynchronous. At the time you get the response, you can check if it's OK and then return the .json(), without waiting in between.
.then(response => {
if (!response.ok) {
throw new Error("Response not ok!");
}
return response.json();
})
.then(data => {

Refactor from fetch to await that can yield same result

So I moved over a non-reusable fetch request code snippet to my API:
let response = await fetch(visitURL, {
method: 'POST',
headers: {
'Content-Type': 'application/json',
'Authorization': 'Bearer ' + userJWT
},
body: JSON.stringify(endingVisit)
});
if (response.ok) {
let {visitId, createdAt} = await response.json();
const viewVisitDto = new ViewVisitDto(`${visitId}${createdAt}${visitorId}${doctorId}${oldPatientId}`);
return viewVisitDto;
} else {
throw new Error("deactivated!")
}
I was able to get this far:
axios.post(visitURL, {
headers,
body: JSON.stringify(visit)
}).then((response) => {
console.log(response);
}).catch((error) => {
console.log(error);
})
But does not exactly give me the visitId and createdAt from the response and I cannot use a response.ok nor a response.json(). Essentially I need to pull out that visitId and createdAt that should be coming back in the response.
I also tried just using node-fetch library, but although in VS code it seems to accept it, TypeScript is not happy with it even when I do install #types/node-fetch and even when I create a type definition file for it, my API just doesn't like it.
Guessing what you are after is
// don't know axios, but if it returns a promise await it
const dto = await axios.post(visitURL, {
headers,
body: JSON.stringify(visit)
}).then((response) => {
// parse response
return {resonse.visitId, resonse.createdAt}
}).then(({visitId, createdAt}) => {
// form dto (where are other vals)?
return new ViewVisitDto(`${visitId}${createdAt}${visitorId}${doctorId}${oldPatientId}`);
}).catch((error) => {
console.log(error);
})
However - you don't mention where doctorId and oldPatientId come from... You try providing more info, including output of the console.log's and the surrounding code

fetchAPI not returning response as then() is getting skipped

I am using fetchAPI to do a post call to my router which will fetch data of logged in user.
Below is the code for the same
submit_button.addEventListener('click',getuser)
function getuser()
{
console.log('clicked')
const username=uname_button.value;
const password=age_button.value;
console.log('username'+username)
console.log('password'+password)
const user = {
email: username,
password: password
};
let options = {
method: 'post',
headers: {
'Content-Type': 'application/json;charset=utf-8'
},
body: JSON.stringify(user)
}
fetch('/users', options)
.then(function(response) {
console.log(response)
})
}
When i execute this in browser, data is getting posted successfully but response is not getting printed , not even promise.
when i added debug points, i could see that control is not going inside then() block?
Can anyone help me with how how to solve this issue?
add a catch block after then to see if any error occurred, as follows:
fetch('/users', options)
.then(function(response) { console.log(response) })
.catch(function(error) { console.log(error) })
Remember that fetch returns a Promise containing the Response object. In order to extract the JSON body content from the response, we use the json() method.
fetch('/users', options)
.then(response => response.json())
.then(data => console.log(data))
.catch((error) => {
console.error('Error:', error);
});

How to console log the whole content of error in the catch block of a fetch call when there is a network failure

I am making a network request in a react native project using the fetch api. It works well in normal conditions but when I am offline the catch block just gives as result of the logging error but when I do err.message I get "Network request failed" I was hoping to get some codes. How can I get the possible codes to check for in anticipation of a network failure?
I tried logging the entire err and I get nothing but when I use err.message I get "Network request failed"
fetch(url, {
method: 'GET',
headers: {
Accept: 'application/json',
'Content-Type': 'application/json',
}
})
.then((response) => response.json())
.then((responseJson) => {
this.setState({ procesing: false });
this.setState({ music: responseJson });
})
.catch(err => {
console.log(err)
console.log(err.message)
})
for console.log(err), I expected to have and error code and the corresponding message but I get nothing
If I understand correctly, you are expecting error for some testing purposes.
First of all, try to console.log any string, like
console.log('error');
If nothing happens (I am pretty sure it won't), try throwing error if response is not okay.
function handleErrors(response) {
if (!response.ok) {
throw Error(response.statusText);
}
return response;
}
fetch("http://httpstat.us/500")
.then(handleErrors)
.then(function(response) {
console.log("ok");
}).catch(function(error) {
console.log(error);
});
Source: https://www.tjvantoll.com/2015/09/13/fetch-and-errors/
As per this answer, you can use a function to stringify the error:
var stringifyError = function(err, filter, space) {
var plainObject = {};
Object.getOwnPropertyNames(err).forEach(function(key) {
plainObject[key] = err[key];
});
return JSON.stringify(plainObject, filter, space);
};
stringifyError(someError, null, '\t');

catching error body using axios post

I am sending a status code 422 from my backend code with response body which contains the description of the error. I am using axios post as below to post a request:
post: function(url, reqBody) {
const request = axios({
baseURL: config.apiUrl,
url: url,
headers: {
'Content-Type': 'application/json',
'Authorization': sessionStorage.getItem('token')
},
method: 'POST',
data: reqBody,
responseType: 'json'
});
return request
.then((res) => {
return res;
})
.catch((error) => {
console.log(error);
return error;
})
}
The problem is when backend is returning error code 422, the error object I am catching has no information about response body. Is there any way I can retrieve the error text?
I had this same issue and the answer (as per Axios >= 0.13) is to specifically check error.response.data:
axios({
...
}).then((response) => {
....
}).catch((error) => {
if( error.response ){
console.log(error.response.data); // => the response payload
}
});
See here for more details.
The "body" of an AXIOS error response depends from the type of response the request had.
If you would like full details about this issue you can see this blogpost: How to catch the body of an error in AXIOS.
In summary AXIOS will return 3 different body depending from the error:
Wrong request, we have actually done something wrong in our request (missing argument, bad format), that is has not actually been sent. When this happen, we can access the information using error.message.
axios.get('wrongSetup')
.then((response) => {})
.catch((error) => {
console.log(error.message);
})
Bad Network request: This happen when the server we are trying to reach does not respond at all. This can either be due to the server being down, or the URL being wrong.
In this case, we can access the information of the request using error.request.
axios.get('network error')
.then((response) => {})
.catch((error) => {
console.log(error.request );
});
Error status: This is the most common of the request. This can happen with any request that returns with a status that is different than 200. It can be unauthorised, not found, internal error and more. When this error happen, we are able to grasp the information of the request by accessing the parameter specified in the snippets below. For the data (as asked above) we need to access the error.response.data.
axios.get('errorStatus')
.then((response) => {})
.catch((error) => {
console.log(error.response.data);
console.log(error.response.status);
console.log(error.response.headers);
})
For those using await/async and Typescript
try {
const response = await axios.post(url, body)
} catch (error) {
console.log(error.response.data);
}
For react native it just worked for me
api.METHOD('endPonit', body)
.then(response => {
//...
})
.catch (error => {
const errorMessage = JSON.parse(error.request.response)
console.log(errorMessage.message)
})
We can check error.response.data as #JoeTidee said. But in cases response payload is blob type? You can get error response body with the below code.
axios({
...
}).then((response) => {
....
}).catch(async (error) => {
const response = error.response
if(typeof response.data.text === function){
console.log(await response.data.text()); // => the response payload
} else {
console.log(response.data)
}
});
I am returning a string from backend but expecting a json as response type. So I need to return an object instead of string for axios to process it properly.
In my case I wanted to retrieve a response 404 error message (body).
I got body with error.response.data but I couldn't display it because the type was ArrayBuffer.
Solution:
axios.get(url, { responseType: 'arraybuffer' }).then(
response => {...},
error => {
const decoder = new TextDecoder()
console.log(decoder.decode(error.response.data))
}
)
Related posts:
Converting between strings and ArrayBuffers

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