Here my code:

let xhr;

function uploadFile() {
    const bar = $("#progressUpload");
    const dialog = $("#modalUpload");
    const alertOk = $("#alertUploadOk");
    const btnClose = $("#btnClose");
    const btnAbort = $("#btnAbort");

    dialog.modal("show");
    btnClose.prop("disabled", true);
    btnAbort.prop("disabled", false);

    xhr = $("#formUploadConfig").ajaxForm({  // <--- does not store the Ajax call
        beforeSubmit: function() {
            let percentVal = '0%';
            bar.width(percentVal)
            bar.html(percentVal).attr('aria-valuenow', percentVal);
        },

        uploadProgress: function(event, position, total, percentComplete) {
            let percentVal = percentComplete + '%';
            bar.width(percentVal)
            bar.html(percentVal).attr('aria-valuenow', percentVal);
        },

        success: function(response) {
            let percentVal = '100%';
            bar.width(percentVal)
            bar.html(percentVal).attr('aria-valuenow', percentVal);
            alertOk.show();
        },

        complete: function(xhr) {
            if (xhr.responseText) {
                btnClose.prop("disabled", false);
                btnAbort.prop("disabled", true);
            }
        },

        abort: function () {
            alert("aborted");
        }
    });
}

My goal is to store the Ajax call in order to call xhr.abort(); as needed. If I was using the standard ajax function I was simple:

var xhr = $.ajax({ ...

but now I'm trying to use the JQuery AjaxForm plugin and I don't understand how to retrieve this variable.