I tried a ReactJS fetch call to a REST-API and want to handle the response. The call works, i get a response, which i can see in Chrome Dev Tools:
function getAllCourses() {
fetch('http://localhost:8080/course', {
method: 'POST',
mode: 'no-cors',
credentials: 'same-origin',
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json',
},
body: JSON.stringify({
objectClass: 'course',
crud: '2'
})
}).then(function (response) {
console.log(response);
return response.json();
}).catch(function (err) {
console.log(err)
});
}
When i try to handle the response, i got a "SyntaxError: Unexpected end of input" at
return response.json();
The console.log looks like this:
My Response JSON looks like this, it is valid, i checked it with jsonlint:
[
{
"0x1": {
"users": [],
"lectures": [],
"owner": "0x2",
"title": "WWI 14 SEA",
"description": null,
"objectClass": "course",
"id": "course_00001"
},
"0x2": {
"username": "system",
"lectures": [],
"course": null,
"solutions": [],
"exercises": [],
"roles": [
"0x3",
"0x4",
"0x5"
],
"objectClass": "user",
"id": "user_00001"
},
"0x3": {
"roleName": "ROLE_ADMIN",
"objectClass": "role",
"id": "role_00001"
},
"0x4": {
"roleName": "ROLE_STUDENT",
"objectClass": "role",
"id": "role_00002"
},
"0x5": {
"roleName": "ROLE_DOCENT",
"objectClass": "role",
"id": "role_00003"
}
}
]
You need to remove the mode: 'no-cors'
setting from your request. Setting no-cors
mode is exactly the cause of the problem you’re having.
A no-cors
request makes the response type opaque
. The log snippet in the question shows that. And opaque
means your frontend JavaScript code can’t see the response body or headers.
https://developer.mozilla.org/en-US/docs/Web/API/Request/mode explains:
no-cors
— JavaScript may not access any properties of the resultingResponse
So the effect of setting no-cors
mode is essentially to tell browsers, “Don’t let frontend JavaScript code access the response body or headers under any circumstances.”
I imagine you’re trying no-cors
because the response from http://localhost:8080/course
doesn’t include the Access-Control-Allow-Origin
response header or else because your request is one that triggers a CORS preflight, and so your browser’s doing an OPTIONS
preflight.
But using no-cors
mode is not the solution to those problems. The solution is either to:
configure the http://localhost:8080
server to send the Access-Control-Allow-Origin
response header and to handle the OPTIONS
request
or set up a CORS proxy using code from https://github.com/Rob--W/cors-anywhere/ or such (see the How to use a CORS proxy to get around “No Access-Control-Allow-Origin header” problems section of the answer at No 'Access-Control-Allow-Origin' header is present on the requested resource—when trying to get data from a REST API)