Ember Ajax request doesn't wait for the response

Here I'm calling an AJAX request with this "Security.createAuthenticatedAjaxRequest(session, URL)" method and I want to return the response of that request. But, it seems like the response doesn't wait until the request completes. It returns undefined as the response. I think it's because it returns the response before ajax request completes.

function minAndMaxGradeAllowedRequest(session) {   if (Common.isEmpty(minAndMaxGradeAllowed)) {
        Security.createAuthenticatedAjaxRequest(session, URL).then(function(minAndMaxGradeAllowedResponse) {
          minAndMaxGradeAllowed = minAndMaxGradeAllowedResponse;
        }).fail(function(error) {
          LOGGER('Failed to find Shaywitz Min and Max grades information', error.toString());
        });   }   return minAndMaxGradeAllowed; }





createAuthenticatedAjaxRequest: function(session, url, config){
        if(Common.isEmpty(config)) {
          config = {};
        }
      return this.createAuthenticatedAjaxRequestWithAcceptHeaderParam(session, url, config, true);
    },
    createAuthenticatedAjaxRequestWithAcceptHeaderParam: function(session, url, config, isAcceptRequired){
        if(Common.isEmpty(config)) {
            config = {};
        }

        if(Common.isEmpty(config.headers)) {
            config.headers = {};
        }

        config.headers['Authorization'] = 'Bearer ' + session.get('data.authenticated.access_token');
        if(!Common.isEmpty(isAcceptRequired) &&  isAcceptRequired  === true) {
          config.headers['Accept'] = 'application/json';
        }

        if(Common.isNotEmpty(session.get('data.authenticated.supportuser'))){
          config.headers['supportuser'] = session.get('data.authenticated.supportuser');
        }

        return Ember.$.ajax(url, config);
    },

Below is the code where it uses the response of the function minAndMaxGradeAllowedRequest(session).

let minAndMaxGradeAllowed = ShaywitzGradesAllowed.getMinAndMaxGradeAllowed(this.get('session'));

I don't have much experience with Ember js. Can someone please help me to solve this problem?