Showing ribbon button based on the result of async operation – Andrew Butenko’s Blog

var AccountRibbon = (function () {

    //this variable stores if async operation was already completed

    var isAsyncOperationCompleted = false;

    //this variable stores the result – if button enabled or not

    var isButtonEnabled = false;

    function IsButtonEnabled(formContext) {

        //If async operation was already completed I just return the result of it