Using XHR instead of the fetch API is not out of the question. Fetch isn't a 1:1 replacement, and as Chris Ferdinandi points out, requires two functions just to get the data in readable form. (In the first then() the data is in a stream.) Another great post by Glenn Stovall demonstrates how to write a small ajax function using XHR without any third party libraries.
You're not wrong, and the extra step is a bit misunderstood, although important if you want to stream large binary files (I used it in this PWA demo to show a %—blink and you'll miss it).
I have a few unrelated thoughts:
responseType = 'json'
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