TypeError: Failed to execute 'fetch' on 'Window': Invalid value

Question

I\'ve tried to use fetch to call from backend using react, without libs (such as Axios). So I created this function:

export function api(url, method, body, i         


        

Answer 1

In my case it occurred because I wrote "Content Type" instead of "Content-Type"

Answer 2

I got the same problem, but working with Angular 7, I was using a Interceptor service like this:

// headerservice.ts
public intercept() {
    const token = Cookies.get('token');
    this.Language = Cookies.get('language');
    this.headers = new HttpHeaders(
      {
        Authorization: 'JWT ' + token,
        'Accept-Language': this.Language
      }
    );
    return this.headers;
  }

  //other file 
   this.headers = this.headersService.intercept();

But it doesn´t work on the other file where i am doing the fetch, so i remove the service and put the headers directly inside the function and it works! like this:

const token = Cookies.get('token');
const language = Cookies.get('language');
const headers = { 
 Authorization: 'JWT ' + token,
'Accept-Language': language
}
const fetchParams = { method: 'GET',
           headers: (headers) };
fetch(url, fetchParams)