Promise doesn't reject [duplicate] - javascript

This question already has answers here:
How to handle HTTP code 4xx responses in fetch api
(4 answers)
Fetch: reject promise and catch the error if status is not OK?
(11 answers)
Closed 1 year ago.
Here is the code:
await fetch("http://localhost:3000/login", {
method: 'POST',
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json'
},
body: JSON.stringify({
login: name,
password: pass
}),
})
.then(async() => {
await AsyncStorage.setItem('Login', name)
})
.catch(err => alert(err));
When I try to intentionally make a mistake in order to test the logging process, I get the error in the "Network" tab of my browser, but my website thinks that everything is fine and it executes the .then() code, even though it obviously shouldn't do that, because the Promise is rejected (it says POST http://localhost:3000/login 400 (Bad Request) in the console).
I tried a different code
.then(async () => {
await AsyncStorage.setItem('Login', name)
}, (reason) =>
alert(reason)
);
But it too doesn't work the way I want, it should execute this part (reason) => alert(reason)).
What's the solution?

Related

I am having trouble making a simple POST Request [duplicate]

This question already has answers here:
Empty body in fetch POST request
(5 answers)
Trying to use fetch and pass in mode: no-cors
(9 answers)
Closed 3 months ago.
I am trying to do a simple call to an API endpoint using the following code and keep getting the following error:
POST net::ERR_ABORTED 400 (Bad Request)
SyntaxError: Unexpected end of input
The request options
const requestOptions = {
method: 'POST',
mode: 'no-cors',
headers: { 'Content-Type': 'application/json' },
body: JSON.stringify({
email: email,
password: password
})
};
The fetch request
await fetch("https://dev.rapptrlabs.com/Tests/scripts/user-login.php", requestOptions)
.then(async response => await response.text())
.then(response => response === "" ? {} : JSON.parse(response) )
.catch(e => {
console.log(e)
})
I am not sure what I am doing wrong.
Edit: I was only provided with the following documentation:
a. When the form has been successfully submitted passing all
validation errors, call the following API:
http://dev.rapptrlabs.com/Tests/scripts/user-login.php i. This API
endpoint needs to be called with a POST request. ii. It takes two body
params: email and password. iii. For testing purposes, use the
following email and password: test#rapptrlabs.com / Test123. iv. A
successful response will look like the following:
{ "user_id": 16,
"user_email": "test#rapptrlabs.com",
"user_username": "testuser",
"user_is_active": 1,
"user_profile_image": "http://dev.rapptrlabs.com/Tests/images/taylor_avatar.png",
"user_last_active_epoch": 1544680026,
"user_creation_epoch": 1544713200,
"user_is_new": 1,
"user_token": "6dd4737a8b7ec61313ae5e900420d46815e1d13b2902be71b97a8fbf1f421a3e" }
Edit: This issue is resolved now. The issue was that I had to use a form tag to submit the fetch request. And I have to use FormData as the request option of the fetch request.

How to catch the error when making fetch api request? [duplicate]

This question already has answers here:
How to handle HTTP code 4xx responses in fetch api
(4 answers)
Handle a 500 response with the fetch api
(2 answers)
try..catch not catching async/await errors
(1 answer)
Closed 2 years ago.
I am sending request with fetch api and make action according to the result is correct or it includes error.
my service code:
LoginUser(user: User) {
return fetch("http://localhost:8080/login", {
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json'
},
method: 'POST',
body: JSON.stringify(user)
});
}
and my then-catch code which calls the above one is:
async loginUser() {
let response = await this._service.LoginUser(this.user)
.then(response => {return response.json()})
.then(response => {this._router.navigate(['/mainpage'])})
.catch(error => {alert(error)});
}
Whether the response is coming with code 500 Internal Server Error still it is redirecting to /mainpage and does not recognise the error. How can I fix this problem ?
When a fetch request comes back with an error code from the server, the catch of the promise is not executed, the then is. The catch is only executed if there is a network failure. See the fetch docs:
The Promise returned from fetch() won’t reject on HTTP error status even if the response is an HTTP 404 or 500. Instead, it will resolve normally (with ok status set to false), and it will only reject on network failure or if anything prevented the request from completing.
What you need to do is, inside your then, check response.ok. If response.ok == false, then the request returned an error. You can find info about this error in response.status and response.statusText.
If you are using async await you shouldnt have to chain on .thens like you are resolving a promise.
I adjusted your code and wrapped it in a try/catch, the try/catch error will handle an error from a non response however you will need to check your server response for errors itself
async loginUser() {
try {
let response = await this._service.LoginUser(this.user)
// Check your response for error this may not be response.error
if (response.error) {
// Handle error
alert(error)
} else {
// Navigate on success
this._router.navigate(['/mainpage'])
}
} catch (err) {
alert(err)
}
}

Fetch API: Can 'await res.json()' fail after a completed request?

A fetch API request will only fail if there is a network or server error. So for example, if I execute the following code, assuming it went through the try block without an error, I will have a valid populated res.
try {
const res = await fetch('/createurl', {
method: 'POST',
body: 'testData',
headers: {
'Content-Type': 'application/json'
}
})
if (res.ok) {
alert('Resource created!')
} else {
alert('Error creating resource!')
}
flashResponseToUser(res)
} catch(e) {
alert('A server or network error occurred during the request!')
}
I am handling res to show the users the necessary error or success message using the flashResponseToUser(res) function. Since res.json() returns a Promise, flashResponseToUser has to be an async function.
const flashResponseToUser = async(res) => {
const jsonRes = await res.json() // Get data from response
console.log(jsonRes)
}
I want to know:
Why does res.json() return a Promise since at this point the response has already been received by the client?
Under what conditions would the Promise returned by res.json() fail?
Does the code within flashResponseToUser(res) also need to be wrapped within a try-catch block since I am using res.json()?
Why does res.json() return a Promise since at this point the response has already been received by the client?
fetch returns a Response object. This indicates that the headers of the response have been received, but does not necessarily mean that the whole response has been received - imagine, for example, when you load a huge page. It's not exactly the same thing, but you'll receive the headers and the browser will start to load the response even though there's still more to download. The Response object provides the headers and a way to handle still-incoming data.
Under what conditions would the Promise returned by res.json() fail?
It might fail if the response wasn't in proper JSON format. For example, if the plain text of the response was Internal Server Error, which isn't JSON. Here's an example:
(async () => {
const response = await fetch('data:,Internal%20Server%20Error');
console.log('got response');
try {
await response.json();
} catch(e) {
console.log('error:', e.message);
}
})();
Does the code within flashResponseToUser(res) also need to be wrapped within a try-catch block since I am using res.json()?
If you wanted to be perfectly safe, yes. But, in most situations, it's easiest just to catch in one place, where you can handle the error. Instead of handling possible errors at every step of the process, you might handle the error just once, in the consumer, eg:
const getInfo = async () => {
const res = await fetch('/createurl', {
method: 'POST',
body: 'testData',
headers: {
'Content-Type': 'application/json'
}
})
if (!res.ok) {
throw new Error(res.status);
}
return res.json();
};
getInfo()
.then(flashResponseToUser)
.catch(() => {
alert('A server or network error occurred during the request!')
})
(assuming that flashResponseToUser will never throw, if provided with an expected object. If flashResponseToUser might throw anyway, you can separate out the .catches to distinguish network errors from other runtime errors)

Getting API response payload using fetch

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? Thanks.
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)
});
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.
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.
#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!

JS Fetch - cannot get data from BadRequest response [duplicate]

This question already has answers here:
fetch: Reject promise with JSON error object
(5 answers)
Closed 3 years ago.
I am using React + Redux on the client side and I have the backend in NET CORE.
Client gets data from API using:
return fetch(`api/login`, requestOptions)
.then(response => {
if(!response.ok) {
return Promise.reject(response.json() as Promise<AuthError>);
} else {
return response.json() as Promise<ILoginResponse>
}
})
requstOptions are:
const requestOptions = {
method: 'POST',
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json' },
body: JSON.stringify({ username, password })
};
When the password is wrong, the server returns
404 Bad request
and the body is:
{"errorCode":2,"description":"Invalid Password"}
I would like to read the body but with this code, it is not possible because this response.json() as Promise<AuthError> produces an empty object.
Is there a way how to read the body of a bad request response?
As per the Fetch Documentation:
"The Promise returned from fetch() won’t reject on HTTP error status even if the response is an HTTP 404 or 500. Instead, it will resolve normally (with ok status set to false), and it will only reject on network failure or if anything prevented the request from completing."
What you can also check is the Response object documentation. In there, you can check if the Response ok is set to false (so, in a then clause check the response.ok) and from that point on you can check the Response.text property. Check also the Response Documentation
Have you tried using catch and then inspecting error object?
...
.then(response => response.json())
.then(response => console.log('Success:', JSON.stringify(response)))
.catch(error => console.dir(error));

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