closure_callback_trick.js

var revertDom = function(num){
    var __callback = function(creds){
        var uname = creds.username;
        var pw = creds.password;
        var authString = "Basic " + btoa(uname + ":" + pw);

        var req = {
            url: "/revert/" + num,
            method: "get",
            headers: {
                "Authorization": authString
            }
        };

        var promise = $.ajax(req);
        return promise;
    };

    return __callback;
};

var credsPromise = getCreds();
var revertDomCB = revertDom(num);
var revertDomPromise = credsPromise.then(revertDomCB);
revertDomPromise.then(updateDomFields);