vanilla_js_cancelable_ajax.js

$request = null;

$('form').on('submit', function(event) {
    event.preventDefault();

    if ($request != null) {
        $request.abort();
        $request = null;
    }
    
    $request = $.ajax({
        // ...
        error: function(err) {
            if (err.statusText =='abort') {
                return;
            }
        }
    });
});