I want to get "msg.sheet" and "msg.instance_url" out of the following code:

function checkT() {
    $(window).on("message", async function (event) {
        let origin = event.origin || event.originalEvent.origin;
        if (origin !== "https://***.***.com") return;
        let msg = event.data || event.originalEvent.data;
        if (msg.sheet == 'undefined') {
            client.invoke('notify', 'You must login in.');
        } else {
            return {
            sheet: msg.sheet,
            instance_url: msg.instance_url
        }
        }
    })
}

let data = checkT()
console.log(data) // {sheet: msg.sheet, instance_url: msg.instance_url}

can it be solved with promises?