fetch to call badrequest message from dotnet [duplicate] - javascript

Here's what I have going:
import 'whatwg-fetch';
function fetchVehicle(id) {
return dispatch => {
return dispatch({
type: 'FETCH_VEHICLE',
payload: fetch(`http://swapi.co/api/vehicles/${id}/`)
.then(status)
.then(res => res.json())
.catch(error => {
throw(error);
})
});
};
}
function status(res) {
if (!res.ok) {
return Promise.reject()
}
return res;
}
EDIT: The promise doesn't get rejected, that's what I'm trying to figure out.
I'm using this fetch polyfill in Redux with redux-promise-middleware.

Fetch promises only reject with a TypeError when a network error occurs. Since 4xx and 5xx responses aren't network errors, there's nothing to catch. You'll need to throw an error yourself to use Promise#catch.
A fetch Response conveniently supplies an ok , which tells you whether the request succeeded. Something like this should do the trick:
fetch(url).then((response) => {
if (response.ok) {
return response.json();
}
throw new Error('Something went wrong');
})
.then((responseJson) => {
// Do something with the response
})
.catch((error) => {
console.log(error)
});

The following login with username and password example shows how to:
Check response.ok
reject if not OK, instead of throw an error
Further process any error hints from server, e.g. validation issues
login() {
const url = "https://example.com/api/users/login";
const headers = {
Accept: "application/json",
"Content-Type": "application/json",
};
fetch(url, {
method: "POST",
headers,
body: JSON.stringify({
email: this.username,
password: this.password,
}),
})
.then((response) => {
// 1. check response.ok
if (response.ok) {
return response.json();
}
return Promise.reject(response); // 2. reject instead of throw
})
.then((json) => {
// all good, token is ready
this.store.commit("token", json.access_token);
})
.catch((response) => {
console.log(response.status, response.statusText);
// 3. get error messages, if any
response.json().then((json: any) => {
console.log(json);
})
});
},

Thanks for the help everyone, rejecting the promise in .catch() solved my issue:
export function fetchVehicle(id) {
return dispatch => {
return dispatch({
type: 'FETCH_VEHICLE',
payload: fetch(`http://swapi.co/api/vehicles/${id}/`)
.then(status)
.then(res => res.json())
.catch(error => {
return Promise.reject()
})
});
};
}
function status(res) {
if (!res.ok) {
throw new Error(res.statusText);
}
return res;
}

For me,
fny answers really got it all. since fetch is not throwing error, we need to throw/handle the error ourselves.
Posting my solution with async/await. I think it's more strait forward and readable
Solution 1: Not throwing an error, handle the error ourselves
async _fetch(request) {
const fetchResult = await fetch(request); //Making the req
const result = await fetchResult.json(); // parsing the response
if (fetchResult.ok) {
return result; // return success object
}
const responseError = {
type: 'Error',
message: result.message || 'Something went wrong',
data: result.data || '',
code: result.code || '',
};
const error = new Error();
error.info = responseError;
return (error);
}
Here if we getting an error, we are building an error object, plain JS object and returning it, the con is that we need to handle it outside.
How to use:
const userSaved = await apiCall(data); // calling fetch
if (userSaved instanceof Error) {
debug.log('Failed saving user', userSaved); // handle error
return;
}
debug.log('Success saving user', userSaved); // handle success
Solution 2: Throwing an error, using try/catch
async _fetch(request) {
const fetchResult = await fetch(request);
const result = await fetchResult.json();
if (fetchResult.ok) {
return result;
}
const responseError = {
type: 'Error',
message: result.message || 'Something went wrong',
data: result.data || '',
code: result.code || '',
};
let error = new Error();
error = { ...error, ...responseError };
throw (error);
}
Here we are throwing and error that we created, since Error ctor approve only string, Im creating the plain Error js object, and the use will be:
try {
const userSaved = await apiCall(data); // calling fetch
debug.log('Success saving user', userSaved); // handle success
} catch (e) {
debug.log('Failed saving user', userSaved); // handle error
}
Solution 3: Using customer error
async _fetch(request) {
const fetchResult = await fetch(request);
const result = await fetchResult.json();
if (fetchResult.ok) {
return result;
}
throw new ClassError(result.message, result.data, result.code);
}
And:
class ClassError extends Error {
constructor(message = 'Something went wrong', data = '', code = '') {
super();
this.message = message;
this.data = data;
this.code = code;
}
}
Hope it helped.

2021 TypeScript Answer
What I do is write a fetch wrapper that takes a generic and if the response is ok it will auto .json() and type assert the result, otherwise the wrapper throws the response
export const fetcher = async <T>(input: RequestInfo, init?: RequestInit) => {
const response = await fetch(input, init);
if (!response.ok) {
throw response;
}
return response.json() as Promise<T>;
};
and then I'll catch errors and check if they are an instanceof Response. That way TypeScript knows that error has Response properties such as status statusText body headers etc. and I can apply a custom message for each 4xx 5xx status code.
try {
return await fetcher<LoginResponse>("http://localhost:8080/login", {
method: "POST",
headers: {
Accept: "application/json",
"Content-Type": "application/json",
},
body: JSON.stringify({ email: "user#example.com", password: "passw0rd" }),
});
} catch (error) {
if (error instanceof Response) {
switch (error.status) {
case 401:
throw new Error("Invalid login credentials");
/* ... */
default:
throw new Error(`Unknown server error occured: ${error.statusText}`);
}
}
throw new Error(`Something went wrong: ${error.message || error}`);
}
and if something like a network error occurs it can be caught outside of the instanceof Response check with a more generic message i.e.
throw new Error(`Something went wrong: ${error.message || error}`);

The answer by #fny (the accepted answer) didn't work for me. The throw new Error() wasn't getting picked up by the .catch. My solution was to wrap the fetch with a function that builds a new promise:
function my_fetch(url, args) {
return new Promise((resolve, reject) => {
fetch(url, args)
.then((response) => {
response.text().then((body) => {
if (response.ok) {
resolve(body)
} else {
reject(body)
}
})
})
.catch((error) => { reject(error) })
})
}
Now every error and non-ok return will be picked up by the .catch method:
my_fetch(url, args)
.then((response) => {
// Do something with the response
})
.catch((error) => {
// Do something with the error
})

function handleErrors(response) {
if (!response.ok) {
throw Error(response.statusText);
}
return response;
}
fetch("https://example.com/api/users")
.then(handleErrors)
.then(response => console.log("ok") )
.catch(error => console.log(error) );

I wasn't satisfied with any of the suggested solutions, so I played a bit with Fetch API to find a way to handle both success responses and error responses.
Plan was to get {status: XXX, message: 'a message'} format as a result in both cases.
Note: Success response can contain an empty body. In that case we fallback and use Response.status and Response.statusText to populate resulting response object.
fetch(url)
.then(handleResponse)
.then((responseJson) => {
// Do something with the response
})
.catch((error) => {
console.log(error)
});
export const handleResponse = (res) => {
if (!res.ok) {
return res
.text()
.then(result => JSON.parse(result))
.then(result => Promise.reject({ status: result.status, message: result.message }));
}
return res
.json()
.then(result => Promise.resolve(result))
.catch(() => Promise.resolve({ status: res.status, message: res.statusText }));
};

I just checked the status of the response object:
$promise.then( function successCallback(response) {
console.log(response);
if (response.status === 200) { ... }
});

Hope this helps for me throw Error is not working
function handleErrors(response) {
if (!response.ok) {
return new Promise((resolve, reject) => {
setTimeout(() => {
reject({
status: response.status,
statusText: response.statusText,
});
}, 0);
});
}
return response.json();
}
function clickHandler(event) {
const textInput = input.value;
let output;
fetch(`${URL}${encodeURI(textInput)}`)
.then(handleErrors)
.then((json) => {
output = json.contents.translated;
console.log(output);
outputDiv.innerHTML = "<p>" + output + "</p>";
})
.catch((error) => alert(error.statusText));
}

Another (shorter) version that resonates with most answers:
fetch(url)
.then(response => response.ok ? response.json() : Promise.reject(response))
.then(json => doStuff(json)) //all good
//next line is optional
.catch(response => handleError(response)) //handle error

Related

How to rewrite a fetch request with the possibility of getting an error? [duplicate]

Here's what I have going:
import 'whatwg-fetch';
function fetchVehicle(id) {
return dispatch => {
return dispatch({
type: 'FETCH_VEHICLE',
payload: fetch(`http://swapi.co/api/vehicles/${id}/`)
.then(status)
.then(res => res.json())
.catch(error => {
throw(error);
})
});
};
}
function status(res) {
if (!res.ok) {
return Promise.reject()
}
return res;
}
EDIT: The promise doesn't get rejected, that's what I'm trying to figure out.
I'm using this fetch polyfill in Redux with redux-promise-middleware.
Fetch promises only reject with a TypeError when a network error occurs. Since 4xx and 5xx responses aren't network errors, there's nothing to catch. You'll need to throw an error yourself to use Promise#catch.
A fetch Response conveniently supplies an ok , which tells you whether the request succeeded. Something like this should do the trick:
fetch(url).then((response) => {
if (response.ok) {
return response.json();
}
throw new Error('Something went wrong');
})
.then((responseJson) => {
// Do something with the response
})
.catch((error) => {
console.log(error)
});
The following login with username and password example shows how to:
Check response.ok
reject if not OK, instead of throw an error
Further process any error hints from server, e.g. validation issues
login() {
const url = "https://example.com/api/users/login";
const headers = {
Accept: "application/json",
"Content-Type": "application/json",
};
fetch(url, {
method: "POST",
headers,
body: JSON.stringify({
email: this.username,
password: this.password,
}),
})
.then((response) => {
// 1. check response.ok
if (response.ok) {
return response.json();
}
return Promise.reject(response); // 2. reject instead of throw
})
.then((json) => {
// all good, token is ready
this.store.commit("token", json.access_token);
})
.catch((response) => {
console.log(response.status, response.statusText);
// 3. get error messages, if any
response.json().then((json: any) => {
console.log(json);
})
});
},
Thanks for the help everyone, rejecting the promise in .catch() solved my issue:
export function fetchVehicle(id) {
return dispatch => {
return dispatch({
type: 'FETCH_VEHICLE',
payload: fetch(`http://swapi.co/api/vehicles/${id}/`)
.then(status)
.then(res => res.json())
.catch(error => {
return Promise.reject()
})
});
};
}
function status(res) {
if (!res.ok) {
throw new Error(res.statusText);
}
return res;
}
For me,
fny answers really got it all. since fetch is not throwing error, we need to throw/handle the error ourselves.
Posting my solution with async/await. I think it's more strait forward and readable
Solution 1: Not throwing an error, handle the error ourselves
async _fetch(request) {
const fetchResult = await fetch(request); //Making the req
const result = await fetchResult.json(); // parsing the response
if (fetchResult.ok) {
return result; // return success object
}
const responseError = {
type: 'Error',
message: result.message || 'Something went wrong',
data: result.data || '',
code: result.code || '',
};
const error = new Error();
error.info = responseError;
return (error);
}
Here if we getting an error, we are building an error object, plain JS object and returning it, the con is that we need to handle it outside.
How to use:
const userSaved = await apiCall(data); // calling fetch
if (userSaved instanceof Error) {
debug.log('Failed saving user', userSaved); // handle error
return;
}
debug.log('Success saving user', userSaved); // handle success
Solution 2: Throwing an error, using try/catch
async _fetch(request) {
const fetchResult = await fetch(request);
const result = await fetchResult.json();
if (fetchResult.ok) {
return result;
}
const responseError = {
type: 'Error',
message: result.message || 'Something went wrong',
data: result.data || '',
code: result.code || '',
};
let error = new Error();
error = { ...error, ...responseError };
throw (error);
}
Here we are throwing and error that we created, since Error ctor approve only string, Im creating the plain Error js object, and the use will be:
try {
const userSaved = await apiCall(data); // calling fetch
debug.log('Success saving user', userSaved); // handle success
} catch (e) {
debug.log('Failed saving user', userSaved); // handle error
}
Solution 3: Using customer error
async _fetch(request) {
const fetchResult = await fetch(request);
const result = await fetchResult.json();
if (fetchResult.ok) {
return result;
}
throw new ClassError(result.message, result.data, result.code);
}
And:
class ClassError extends Error {
constructor(message = 'Something went wrong', data = '', code = '') {
super();
this.message = message;
this.data = data;
this.code = code;
}
}
Hope it helped.
2021 TypeScript Answer
What I do is write a fetch wrapper that takes a generic and if the response is ok it will auto .json() and type assert the result, otherwise the wrapper throws the response
export const fetcher = async <T>(input: RequestInfo, init?: RequestInit) => {
const response = await fetch(input, init);
if (!response.ok) {
throw response;
}
return response.json() as Promise<T>;
};
and then I'll catch errors and check if they are an instanceof Response. That way TypeScript knows that error has Response properties such as status statusText body headers etc. and I can apply a custom message for each 4xx 5xx status code.
try {
return await fetcher<LoginResponse>("http://localhost:8080/login", {
method: "POST",
headers: {
Accept: "application/json",
"Content-Type": "application/json",
},
body: JSON.stringify({ email: "user#example.com", password: "passw0rd" }),
});
} catch (error) {
if (error instanceof Response) {
switch (error.status) {
case 401:
throw new Error("Invalid login credentials");
/* ... */
default:
throw new Error(`Unknown server error occured: ${error.statusText}`);
}
}
throw new Error(`Something went wrong: ${error.message || error}`);
}
and if something like a network error occurs it can be caught outside of the instanceof Response check with a more generic message i.e.
throw new Error(`Something went wrong: ${error.message || error}`);
The answer by #fny (the accepted answer) didn't work for me. The throw new Error() wasn't getting picked up by the .catch. My solution was to wrap the fetch with a function that builds a new promise:
function my_fetch(url, args) {
return new Promise((resolve, reject) => {
fetch(url, args)
.then((response) => {
response.text().then((body) => {
if (response.ok) {
resolve(body)
} else {
reject(body)
}
})
})
.catch((error) => { reject(error) })
})
}
Now every error and non-ok return will be picked up by the .catch method:
my_fetch(url, args)
.then((response) => {
// Do something with the response
})
.catch((error) => {
// Do something with the error
})
function handleErrors(response) {
if (!response.ok) {
throw Error(response.statusText);
}
return response;
}
fetch("https://example.com/api/users")
.then(handleErrors)
.then(response => console.log("ok") )
.catch(error => console.log(error) );
I wasn't satisfied with any of the suggested solutions, so I played a bit with Fetch API to find a way to handle both success responses and error responses.
Plan was to get {status: XXX, message: 'a message'} format as a result in both cases.
Note: Success response can contain an empty body. In that case we fallback and use Response.status and Response.statusText to populate resulting response object.
fetch(url)
.then(handleResponse)
.then((responseJson) => {
// Do something with the response
})
.catch((error) => {
console.log(error)
});
export const handleResponse = (res) => {
if (!res.ok) {
return res
.text()
.then(result => JSON.parse(result))
.then(result => Promise.reject({ status: result.status, message: result.message }));
}
return res
.json()
.then(result => Promise.resolve(result))
.catch(() => Promise.resolve({ status: res.status, message: res.statusText }));
};
I just checked the status of the response object:
$promise.then( function successCallback(response) {
console.log(response);
if (response.status === 200) { ... }
});
Hope this helps for me throw Error is not working
function handleErrors(response) {
if (!response.ok) {
return new Promise((resolve, reject) => {
setTimeout(() => {
reject({
status: response.status,
statusText: response.statusText,
});
}, 0);
});
}
return response.json();
}
function clickHandler(event) {
const textInput = input.value;
let output;
fetch(`${URL}${encodeURI(textInput)}`)
.then(handleErrors)
.then((json) => {
output = json.contents.translated;
console.log(output);
outputDiv.innerHTML = "<p>" + output + "</p>";
})
.catch((error) => alert(error.statusText));
}
Another (shorter) version that resonates with most answers:
fetch(url)
.then(response => response.ok ? response.json() : Promise.reject(response))
.then(json => doStuff(json)) //all good
//next line is optional
.catch(response => handleError(response)) //handle error

fetch() not catching custom error message

I have the following fetch() api but the catch blocks aren't working correctly. The error message I get is:
SyntaxError: Unexpected token < in JSON at position 0 undefined
but what I'm expecting is:
something went wrong null
here's the api:
const getBtn = document.getElementById('get-btn')
const postBtn = document.getElementById('post-btn')
const sendHttpRequest = (method, url, data) => {
return fetch(url, {
method: method,
body: JSON.stringify(data),
headers: data ? {'Content-Type': 'application/json'} : {}
})
.then(response => {
console.log(response.status)
if(response.status >= 400 || response == null){
return response.json()
.then(errResData => {
const error = new Error('something went wrong')
error.data = errResData
throw error;
})
}
return response.json()
})
}
const getData = () =>{
sendHttpRequest('GET','http://localhost/async/fetch/data.jsonx')
.then(responseData => {
console.log(responseData)
})
.catch(err =>{
console.log(err,err.data)
})
}
const sendData = () =>{
sendHttpRequest('POST','http://localhost/async/fetch/data.phpx',{
email: 'someemail#gmail.com',
password: 'compas'
})
.then(responseData => {
console.log(responseData)
})
.catch(err => {
console.log(err,err.data)
})
}
getBtn.addEventListener('click',getData)
postBtn.addEventListener('click',sendData)
In order to see if a body is parseable as JSON, you need to call .json on the Promise. That will return a Promise that either resolves to the parsed value, or will throw due to the body not being parseable.
If it isn't parseable, .thens connected to it won't run; return response.json().then will not work if the body isn't parseable, so the interpreter never gets to new Error('something went wrong').
.then(response => {
console.log(response.status)
if(response.status >= 400 || response == null){
return response.json()
.then(errResData => {
const error = new Error('something went wrong')
error.data = errResData
throw error;
})
}
return response.json()
should be
.then(response => {
console.log(response.status)
if(response.status >= 400 || response == null){
return response.json()
.catch(errResData => {
const error = new Error('something went wrong')
error.data = errResData
throw error;
})
}
return response.json()
if the non-parseable response will always fulfill the condition response.status >= 400 || response == null.
The throw error inside the .catch in the edited code will result in the Promise rejecting, so getData's .catch will see the error.
If you want to catch an error from a Promise, you should use .catch() instead of .then()

Fetch API POST in React app not logging errors in catch block from express/node server [duplicate]

Here's what I have going:
import 'whatwg-fetch';
function fetchVehicle(id) {
return dispatch => {
return dispatch({
type: 'FETCH_VEHICLE',
payload: fetch(`http://swapi.co/api/vehicles/${id}/`)
.then(status)
.then(res => res.json())
.catch(error => {
throw(error);
})
});
};
}
function status(res) {
if (!res.ok) {
return Promise.reject()
}
return res;
}
EDIT: The promise doesn't get rejected, that's what I'm trying to figure out.
I'm using this fetch polyfill in Redux with redux-promise-middleware.
Fetch promises only reject with a TypeError when a network error occurs. Since 4xx and 5xx responses aren't network errors, there's nothing to catch. You'll need to throw an error yourself to use Promise#catch.
A fetch Response conveniently supplies an ok , which tells you whether the request succeeded. Something like this should do the trick:
fetch(url).then((response) => {
if (response.ok) {
return response.json();
}
throw new Error('Something went wrong');
})
.then((responseJson) => {
// Do something with the response
})
.catch((error) => {
console.log(error)
});
The following login with username and password example shows how to:
Check response.ok
reject if not OK, instead of throw an error
Further process any error hints from server, e.g. validation issues
login() {
const url = "https://example.com/api/users/login";
const headers = {
Accept: "application/json",
"Content-Type": "application/json",
};
fetch(url, {
method: "POST",
headers,
body: JSON.stringify({
email: this.username,
password: this.password,
}),
})
.then((response) => {
// 1. check response.ok
if (response.ok) {
return response.json();
}
return Promise.reject(response); // 2. reject instead of throw
})
.then((json) => {
// all good, token is ready
this.store.commit("token", json.access_token);
})
.catch((response) => {
console.log(response.status, response.statusText);
// 3. get error messages, if any
response.json().then((json: any) => {
console.log(json);
})
});
},
Thanks for the help everyone, rejecting the promise in .catch() solved my issue:
export function fetchVehicle(id) {
return dispatch => {
return dispatch({
type: 'FETCH_VEHICLE',
payload: fetch(`http://swapi.co/api/vehicles/${id}/`)
.then(status)
.then(res => res.json())
.catch(error => {
return Promise.reject()
})
});
};
}
function status(res) {
if (!res.ok) {
throw new Error(res.statusText);
}
return res;
}
For me,
fny answers really got it all. since fetch is not throwing error, we need to throw/handle the error ourselves.
Posting my solution with async/await. I think it's more strait forward and readable
Solution 1: Not throwing an error, handle the error ourselves
async _fetch(request) {
const fetchResult = await fetch(request); //Making the req
const result = await fetchResult.json(); // parsing the response
if (fetchResult.ok) {
return result; // return success object
}
const responseError = {
type: 'Error',
message: result.message || 'Something went wrong',
data: result.data || '',
code: result.code || '',
};
const error = new Error();
error.info = responseError;
return (error);
}
Here if we getting an error, we are building an error object, plain JS object and returning it, the con is that we need to handle it outside.
How to use:
const userSaved = await apiCall(data); // calling fetch
if (userSaved instanceof Error) {
debug.log('Failed saving user', userSaved); // handle error
return;
}
debug.log('Success saving user', userSaved); // handle success
Solution 2: Throwing an error, using try/catch
async _fetch(request) {
const fetchResult = await fetch(request);
const result = await fetchResult.json();
if (fetchResult.ok) {
return result;
}
const responseError = {
type: 'Error',
message: result.message || 'Something went wrong',
data: result.data || '',
code: result.code || '',
};
let error = new Error();
error = { ...error, ...responseError };
throw (error);
}
Here we are throwing and error that we created, since Error ctor approve only string, Im creating the plain Error js object, and the use will be:
try {
const userSaved = await apiCall(data); // calling fetch
debug.log('Success saving user', userSaved); // handle success
} catch (e) {
debug.log('Failed saving user', userSaved); // handle error
}
Solution 3: Using customer error
async _fetch(request) {
const fetchResult = await fetch(request);
const result = await fetchResult.json();
if (fetchResult.ok) {
return result;
}
throw new ClassError(result.message, result.data, result.code);
}
And:
class ClassError extends Error {
constructor(message = 'Something went wrong', data = '', code = '') {
super();
this.message = message;
this.data = data;
this.code = code;
}
}
Hope it helped.
2021 TypeScript Answer
What I do is write a fetch wrapper that takes a generic and if the response is ok it will auto .json() and type assert the result, otherwise the wrapper throws the response
export const fetcher = async <T>(input: RequestInfo, init?: RequestInit) => {
const response = await fetch(input, init);
if (!response.ok) {
throw response;
}
return response.json() as Promise<T>;
};
and then I'll catch errors and check if they are an instanceof Response. That way TypeScript knows that error has Response properties such as status statusText body headers etc. and I can apply a custom message for each 4xx 5xx status code.
try {
return await fetcher<LoginResponse>("http://localhost:8080/login", {
method: "POST",
headers: {
Accept: "application/json",
"Content-Type": "application/json",
},
body: JSON.stringify({ email: "user#example.com", password: "passw0rd" }),
});
} catch (error) {
if (error instanceof Response) {
switch (error.status) {
case 401:
throw new Error("Invalid login credentials");
/* ... */
default:
throw new Error(`Unknown server error occured: ${error.statusText}`);
}
}
throw new Error(`Something went wrong: ${error.message || error}`);
}
and if something like a network error occurs it can be caught outside of the instanceof Response check with a more generic message i.e.
throw new Error(`Something went wrong: ${error.message || error}`);
The answer by #fny (the accepted answer) didn't work for me. The throw new Error() wasn't getting picked up by the .catch. My solution was to wrap the fetch with a function that builds a new promise:
function my_fetch(url, args) {
return new Promise((resolve, reject) => {
fetch(url, args)
.then((response) => {
response.text().then((body) => {
if (response.ok) {
resolve(body)
} else {
reject(body)
}
})
})
.catch((error) => { reject(error) })
})
}
Now every error and non-ok return will be picked up by the .catch method:
my_fetch(url, args)
.then((response) => {
// Do something with the response
})
.catch((error) => {
// Do something with the error
})
function handleErrors(response) {
if (!response.ok) {
throw Error(response.statusText);
}
return response;
}
fetch("https://example.com/api/users")
.then(handleErrors)
.then(response => console.log("ok") )
.catch(error => console.log(error) );
I wasn't satisfied with any of the suggested solutions, so I played a bit with Fetch API to find a way to handle both success responses and error responses.
Plan was to get {status: XXX, message: 'a message'} format as a result in both cases.
Note: Success response can contain an empty body. In that case we fallback and use Response.status and Response.statusText to populate resulting response object.
fetch(url)
.then(handleResponse)
.then((responseJson) => {
// Do something with the response
})
.catch((error) => {
console.log(error)
});
export const handleResponse = (res) => {
if (!res.ok) {
return res
.text()
.then(result => JSON.parse(result))
.then(result => Promise.reject({ status: result.status, message: result.message }));
}
return res
.json()
.then(result => Promise.resolve(result))
.catch(() => Promise.resolve({ status: res.status, message: res.statusText }));
};
I just checked the status of the response object:
$promise.then( function successCallback(response) {
console.log(response);
if (response.status === 200) { ... }
});
Hope this helps for me throw Error is not working
function handleErrors(response) {
if (!response.ok) {
return new Promise((resolve, reject) => {
setTimeout(() => {
reject({
status: response.status,
statusText: response.statusText,
});
}, 0);
});
}
return response.json();
}
function clickHandler(event) {
const textInput = input.value;
let output;
fetch(`${URL}${encodeURI(textInput)}`)
.then(handleErrors)
.then((json) => {
output = json.contents.translated;
console.log(output);
outputDiv.innerHTML = "<p>" + output + "</p>";
})
.catch((error) => alert(error.statusText));
}
Another (shorter) version that resonates with most answers:
fetch(url)
.then(response => response.ok ? response.json() : Promise.reject(response))
.then(json => doStuff(json)) //all good
//next line is optional
.catch(response => handleError(response)) //handle error

Async function returning undefined instead of data

I'm doing requests to my API server to authenticate a user, that's not the problem. The problem is that I don't know why my async function doesn't return anything, and I get an error because the data that I want from this function is undefined.
Don't worry if the error management is ugly and in general I can do this better, I'll do that after fixing this problem.
Utils.js class
async Auth(username, password) {
const body = {
username: username,
password: password
};
let req_uuid = '';
await this.setupUUID()
.then((uuid) => {
req_uuid = uuid;
})
.catch((e) => {
console.error(e);
});
let jwtData = {
"req_uuid": req_uuid,
"origin": "launcher",
"scope": "ec_auth"
};
console.log(req_uuid);
let jwtToken = jwt.sign(jwtData, 'lulz');
await fetch('http://api.myapi.cc/authenticate', {
method: 'POST',
headers: { "Content-Type": "application/json", "identify": jwtToken },
body: JSON.stringify(body),
})
.then((res) => {
// console.log(res);
// If the status is OK (200) get the json data of the response containing the token and return it
if (res.status == 200) {
res.json()
.then((data) => {
return Promise.resolve(data);
});
// If the response status is 401 return an error containing the error code and message
} else if (res.status == 401) {
res.json()
.then((data) => {
console.log(data.message);
});
throw ({ code: 401, msg: 'Wrong username or password' });
// If the response status is 400 (Bad Request) display unknown error message (this sould never happen)
} else if (res.status == 400) {
throw ({ code: 400, msg: 'Unknown error, contact support for help. \nError code: 400' });
}
})
// If there's an error with the fetch request itself then display a dialog box with the error message
.catch((error) => {
// If it's a "normal" error, so it has a code, don't put inside a new error object
if(error.code) {
return Promise.reject(error);
} else {
return Promise.reject({ code: 'critical', msg: error });
}
});
}
Main.js file
utils.Auth('user123', 'admin')
.then((res) => {
console.log(res); // undefined
});
Your Async function must return the last promise:
return fetch('http://api.myapi.cc/authenticate', ...);
or await the result and return it:
var x = await fetch('http://api.myapi.cc/authenticate', ...);
// do something with x and...
return x;
Notice that you don’t need to mix promise syntax (.then) with await. You can, but you don’t need to, and probably shouldn’t.
These two functions do exactly the same thing:
function a() {
return functionReturningPromise().then(function (result) {
return result + 1;
});
}
async function b() {
return (await functionReturningPromise()) + 1;
}
await is not to be used with then.
let data = await this.setupUUID();
or
let data=null;
setupUUID().then(res=> data = res)
I would try something like this:
const postReq = async (jwtToken) => {
const body = {
username: username,
password: password,
};
try {
const res = await fetch('http://api.myapi.cc/authenticate', {
method: 'POST',
headers: { "Content-Type": "application/json", "identify": jwtToken },
body: JSON.stringify(body),
})
if (res) {
if (res.status == 200) {
return res.json();
} else if (res.status == 401) {
const data = res.json();
console.log(data.message)
throw ({ code: 401, msg: 'Wrong username or password' });
} else if (res.status == 400) {
throw ({ code: 400, msg: 'Unknown error, contact support for help. \nError code: 400' });
}
}
} catch (err) {
console.error(err)
}
};
const Auth = async (username, password) => {
const jwtData = {
"origin": "launcher",
"scope": "ec_auth"
};
try {
const req_uuid = await this.setupUUID();
if (req_uuid) {
jwtData["req_uuid"] = req_uuid;
const jwtToken = jwt.sign(jwtData, 'lulz');
return await postReq(jwtToken);
}
} catch (err) {
console.error(err);
};
}

Trying to get data an 'status' from fetch Promise

I am trying to make a generic Fetch method for my React project. The plan is to pass my fetch method a url, and some config data (method, header etc). And then return less technical data to my calling methods. I'd like to return the data from the api call, and the payload, which is json data.
return fetch(URL, config)
.then((response) => {
console.log('Fetch - Got response: ', response);
return response;
})
.then((response) => {
console.log('Json: ', response.status);
const result = { data: response.json(), status: response.status };
return result;
})
.catch((e) => {
console.log(`An error has occured while calling the API. ${e}`);
reject(e);
});
This is my initial attempt, but I'm not quite sure what I'm doing.
my console log that logs 'response', contains the response from the API call:
body: (...)
bodyUsed: true
headers: Headers {}
ok: true
redirected: false
status: 200
statusText: "OK"
type: "cors"
url: "http://localhost:49487//api/xxx/yyy"
So the API call completes, and I get a 200 status.
The line:
console.log('Json: ', response.status);
return 200 as expected.
What I have been doing before is
return response.json()
And then my calling class gets the paylad, but no status. What I am trying to do is return my payload, AND the status.
So I attempted to change it to this:
const result = { data: response.json(), status: response.status };
return result;
But my calling app now sees:
data: Promise {<resolved>: Array(9)}
status: 200
I was expecting to get data: MyPayloadArray, status: 200
I think I'm misunderstanding promises here. (I'm quite green with them).
My data accessor that uses my Fetch method:
static GetAll() {
return new Promise((resolve, reject) => {
const request = {
method: 'GET',
URL: `${Server.ApiURL}/api/admin/clients`,
};
fetchData(request)
.then((result) => {
console.log('GetAll sees response as ', result);
resolve(result);
})
.catch((error) => {
reject(new Error(error));
});
});
}
I'm trying to call my data accessor class, like this:
componentDidMount() {
ClientDataAccessor.GetAll()
.then((response) => {
console.log('Got list!', response);
this.setState({ clients: response, isLoading: false });
})
.catch((error) => {
console.log('Got error on list screen', error);
});
}
How can I get just the status, and the payload back to my DataAccesor class? I think I'm just screwing up the Promises... But not sure of the best pattern here.
I'm going UI class, onComponentDidMount -> DataAccessor.GetAll -> FetchData. I think I'm abusing the Promise somewhere.
The issue here is that response.json() returns another promise. You would have to resolve that promise object yourself and return the object you are looking for.
return fetch(URL, config)
.then((response) => {
console.log('Fetch - Got response: ', response);
return response;
})
.then((response) =>
response.json()
.then( (data) => { data, status: response.status } )
)
.catch((e) => {
console.log(`An error has occured while calling the API. ${e}`);
reject(e);
});
Very ugly...
Why not move it to async/await funtion? All browsers support it at this stage...
async myFetch(URL, config) {
try {
const response = await fetch(URL, config);
console.log('Fetch - Got response:', response);
const data = await response.json();
console.log('Fetch - Got data:', data);
return { data, status: response.status }
}
catch (e) {
console.error(`An error has occured while calling the API. ${e}`);
throw e;
}
}
Just be aware, in both cases, that your function returns another promise.
I think you can solve your issue using Promise.resolve, chaining promise to obtain your result object:
...
.then(response => {
var status = response.status;
return Promise.resolve(response.json())
.then(data => ({ data, status }))
})
The Promise.resolve can take a Promise as parameter and return a promise that will flatten the chain, so you can get the value of the json parse and work with it.
You need to further resolve res.json() to get the info. You can do something like this:
return fetch(URL, config)
.then((response) => {
console.log('Fetch - Got response: ', response);
return response;
})
.then(response =>
response.json().then(json => ({
status: response.status,
json
})
))
.then(({ status, json }) => {
console.log({ status, json });
return { data: json, status: status };
})
.catch((e) => {
console.log(`An error has occured while calling the API. ${e}`);
reject(e);
});
The neat version of above could be:
return fetch(URL, config)
.then(response => response.json()
.then(json => ({ status: response.status, data: json }) )
)
Note: Removed the reject(e) from inside of catch, because it is redundant.

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