Main difference to regular Response and Request types is that no manual JSON.stringify and headers.set('Content-Type', ...) is required.
In my opinion, JSONRequest is the most lightweight way of fixing the biggest issue of the Fetch API when dealing with JSON APIs, without resorting to full alternatives such as superagent or axios.
Example:
const response = await fetch(new JSONRequest('/comments', {
method: 'POST',
body: { text: 'Usage example: ...' },