Conversion of $.ajax call to use fetch (http PUT)

Question

I'm in the process of converting an $.ajax calls to use fetch instead.

I have a PUT call that resembles this (this is an upload of a file from an html form, assume that the "file" object exists and is correct):

const formDataObj = new FormData();
formDataObj.append("file", file, 'test.png');

const settings:any = {
  "url": "https://somedomain.com/upload",
  "method": "PUT",
  "timeout": 0,
  "headers": {
    "Authorization": `Bearer ${token}`
  },
  "processData": false,
  "mimeType": "multipart/form-data",
  "contentType": false,
  "data": formDataObj
}

const result = await $.ajax(settings);

In this case, the "result" shows exactly the result that I would expect. In other words, using jQuery to perform this PUT operation works perfectly. The "result" object contains the correct response from the server, which is a string version of a JSON object.

However, when I attempt to do the same using fetch, it does not work. Here's what I attempted:

const formDataObj = new FormData();
formDataObj.append("file", file, 'test.png');

const settings:any = {
  "method": "PUT",
  "timeout": 0,
  "headers": {
    "Authorization": `Bearer ${token}`
  },
  "processData": false,
  "mimeType": "multipart/form-data",
  "contentType": false,
  "data": formDataObj
}

const response = await fetch('https://somedomain.com/upload', settings);
const data = await response.json();

The "fetch" version shows this error:

Access to fetch at 'https://somedomain.com/upload' from origin 'https://someotherdomain.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

Since the response from the server is JSON represented as a string, not a JSON object, I was thinking that this might be the issue. Or, maybe these libraries treat the "data" property differently?

Since the $.ajax call works exactly was it should, I assume that this is not actually a CORS issue.