I'm genuinely curious to know what you find severely lacking in fetch compared to $.ajax.

- handling cookies

    fetch('https://example.com', { credentials: 'include' })

- HTTP status codes

    fetch('https://example.com').then(response => {
        if (response.ok) {
            // Response is 200-299
        }
        if (response.status === 404) {
            // Status code specific handling
        }
    });

- CORS

    fetch('https://example.com', { mode: 'no-cors' });

- JSON handling

    fetch('https://example.com').then(response => response.json()).then(json => {
        // Do something with a parsed JSON object
    });

I've used all of the above patterns regularly for several years now and never found any of them particularly cumbersome and certainly not lacking feature wise. If async/await syntax is available to you, it's even more succinct than the Promise style above.

With that said, I've not used $.ajax in anger for a good long while so I may be missing out, particularly as I note there have been API changes in newer versions of jQuery. Are there some specific use cases that you've found fetch to be particularly inept in dealing with?