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!
Related
I might be overlooking the obvious but is there a way to get the fetch request? (not the response).
A normal fetch looks like something this:
fetch(url, {
method: method,
headers: new Headers({
'Authorization': token,
'Content-Type': 'application/json'
}),
body: payload
})
.then((response) => response.json())
.then((responseData) => {
console.log(responseData);
})
I want the ability to get the method, headers, body, and are data that are passed to fetch in a variable that can be passed around to other methods like a log.
You can't get the request information from a Response object (the thing the promise from fetch is fulfilled with), but you can build a Request object yourself, pass it around, and then use that with fetch. The Request constructor accepts the same parameters fetch does, but instead of doing the operation, it just returns the Request object for it.
For instance, here's your code done that way:
// Building the request, which you can then pass around
const request = new Request(url, {
method: method,
headers: new Headers({
"Authorization": token,
"Content-Type": "application/json"
}),
body: payload
});
// Using it
fetch(request)
.then((response) => {
if (!response.ok) { // Don't forget this part!
throw new Error(`HTTP error ${response.status}`);
}
return response.json();
})
.then((responseData) => {
console.log(responseData);
});
(Aside: Note the slight addition to the first fulfillment handler above, to handle the fetch API footgun. fetch doesn't reject its promise on HTTP errors, only network errors; you have to check for HTTP errors yourself. More in my blog post here.)
Documentation from Express response.send allows for objects to be sent in the body, which I am sending as follows:
DBM.saveArticle(obj).then((val) => {
console.log(val); // verified here
res.send(val);
res.end();
// ... clip here
However on the client I am not getting the object. This is a Create in CRUD, and I am using fetch POST as follows to implement this.
// ... snip
const options = {
headers: {'Content-Type': 'application/json'},
method: 'POST',
body: JSON.stringify(this.state)
};
fetch("/articles/add", options)
.then((response) => {
console.log('DEBUG: Article Added: ', response); // nothing found here in response
this.props.dispatch({type: 'addArticle', component_state: state});
})
.catch((error) => {
console.log('fetch/POST error', error);
});
// ... snip
console.log from above looks like this, here is a pic, it is empty, as far as I can tell.
The response object is big, and I tried to click all about it, but it is possible I might have missed something.
The official docs for JavaScript fetch response object is here on MDN.
https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch#Response_objects
This is just an HTTP response, not the actual JSON. To extract the JSON body content from the response, we use the json() method (defined on the Body mixin, which is implemented by both the Request and Response objects.)
https://developer.mozilla.org/en-US/docs/Web/API/ReadableStream
The Fetch API offers a concrete instance of a ReadableStream through
the body property of a Response object.
fetch returns the body as a ReadableStream to convert it to a JSON use response.json()
fetch('https://example.com/profile', {
method: 'POST', // or 'PUT'
headers: {
'Content-Type': 'application/json',
},
body: JSON.stringify(data),
})
.then(response => response.json()) // << this will convert the response to JSON object
.then(data => {
console.log('Success:', data);
})
.catch((error) => {
console.error('Error:', error);
});
The data in the ReadableStream is not accessible without consuming the stream, it's stored in a lower-level I/O source, called the underlying source, and there are two types of underlying source: push and pull sources.
In case of HTTP request it's a push source in the form of a TCP socket, where data is constantly being pushed from the OS level, and the data will be accessible to the consumer (your code) once you acquire a lock and start reading it, which is exactly what json() method do for you.
refer to this for more details https://streams.spec.whatwg.org/#rs-model
I am posting request to my backend server using fetch api in React js
const formData = new FormData();
formData.append("image", file);
formData.append("userId", currentUser.id);
formData.append("sliderNumber", sliderNumber);
const myHeaders = new Headers();
myHeaders.append("Content-Type", file.type);
myHeaders.append("Aceess-Control-Allow-Origin", "*");
fetch("http://localhost:4000/upload/slide-image", {
method: "POST",
headers: myHeaders,
mode: "no-cors",
body: formData
})
.then(response => response)
.then(data => console.log("Printing data: ", data));
};
In elixir backend
def upload(conn, params) do
# uploading code
#send response to the client with amazon s3 image url
send_resp(conn, 200, image_url)
end
but Response object from fetch api is empty
Response {
body: null
bodyUsed: false
headers: Headers {}
ok: false
redirected: false
status: 0
statusText: ""
type: "opaque"
url: ""
}
And it doesn't change when I respond with status code 400.
It seems like fetch api is not building Reponse object correctly in some point. Because I can find correct status code and response body in browser network tab. But Response object doesn't hold response from backend server.
Any idea?
If you are expecting a text response from your server, then on your first .then(.. you should do like:
fetch("http://localhost:4000/upload/slide-image", {
method: "POST",
headers: myHeaders,
mode: "no-cors",
body: formData
})
.then(response => response.text()) // <---
.then(data => console.log("Printing data: ", data));
fetch returns a Promise that resolves to a Response. When you use .text() at this stage, what you actually do is to take the Response stream, read it to completion and return a promise that will resolve with a text.
Aside from that, you also use mode: "no-cors" (as other users mentioned on their answers) that limits you in many ways. For example, even if you follow my instructions above, you will get an empty string, even if you are trying to return something from your server. And that will be because of this mode.
You can find more details about it here, under bullet no-cors.
Your Content-Type is wrong. When sending files along with other data, the Content-Type should still be multipart/form-data.
mode: "no-cors",
You set the mode to no-cors, so the response is Opaque, which means you can't see inside it.
Don't do that if you need to read the response.
Asides:
myHeaders.append("Content-Type", file.type);
That's the wrong content-type for a form data object. Don't set the content-type. The fetch API will set the correct one automatically.
myHeaders.append("Aceess-Control-Allow-Origin", "*");
Access-Control-Allow-Origin, which you misspelt, is a response header, not a request header.
.then(response => response)
Returning the response unchanged is rather pointless. You probably want response.text() if you are getting a plain URL back.
The accepted answer solved my pinpoint.
if you are expecting a JSON object from the backend, use
.then((response) => response.json())
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)
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));