Handle response - SyntaxError: Unexpected end of input when using mode: 'no-cors'

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. 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 resulting Response

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 does 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)

In your then you should check if the response is OK before returning response.json:

.then(function (response) {    if (!response.ok) {        return Promise.reject('some reason');    }    return response.json();})

If you want to have the error message in your rejected promise, you can do something like:

.then(function (response) {    if (!response.ok) {       return response.text().then(result => Promise.reject(new Error(result)));    }    return response.json();})

I know this answer might be super late and might have been resolved but i just had the same issue today and I just needed to add a ',' at the end of the headers hash and i stopped getting the error

export function addContacts(formData) {  return(dispatch) => {    dispatch({type: 'POSTING_CONTACTS'});    console.log(formData)    return fetch(uri, {      method: 'POST',      body: JSON.stringify({contact: {name: formData.name, phone_number: formData.phoneNumber}}),      headers: {        Accept: 'application/json',        'Content-Type': 'application/json'      },    })    .then(response => {        return response.json()      }).then(responseJSON => {        console.log(responseJSON)        return dispatch({type: 'ADD_CONTACT', payload: responseJSON});      })  }}