Request.formData()

The formData() method of the Request interface reads the request body and returns it as a promise that resolves with a FormData object.

Exceptions: TypeError Thrown for one of the following reasons: The request body is disturbed or locked. There was an error decoding the body content (for example, because the Content-Encoding header is incorrect). The MIME type of the body cannot be determined from the Content-Type headers included in the request, or is not application/x-www-form-urlencoded or multipart/form-data. The body cannot be parsed as a FormData object.