var token = <TOKEN>;
  var clientId = '1';
  var start = new Promise(
    function (resolve, reject) {
      if (window.Sigma) {
        var sigma = new Sigma();
        var userData = {
          userId: clientId
        };
        sigma.init({ token: token, userData: userData });
        var exp = sigma.getExperiment('exp');
        resolve(exp);
      }else {
        var reason = new Error("s haven't initialized");
        reject(reason);
      }
    }
  );
  var abStart = function () {
      start
        .then(function (res) {
          var resultExp = res.getFeatureValue('test');
          console.log(resultExp);
        })
        .catch(function (error) {
          console.log(error.message);
        });
    };
  abStart();