AWS Cognito - offline data availability

I am building a phonegap app and use AWS Cognito to store the User data. In the description of Cognito, it is said, that the data is offline available. This does not work in my code:

function getCognitoData(){
 var params = {
  IdentityPoolId: COGNITO_IDENTITY_POOL_ID,
  Logins: {
   'graph.facebook.com': FACEBOOK_TOKEN
  }  
 };
 AWS.config.region = AWS_REGION;
 AWS.config.credentials = new AWS.CognitoIdentityCredentials(params);
 AWS.config.credentials.get(function(err) {
  if (err) {
   console.log("Error: "+err);
   return;
  }
  console.log("Cognito Identity Id: " + AWS.config.credentials.identityId);

  var syncClient = new AWS.CognitoSyncManager();

  syncClient.openOrCreateDataset('myDataset', function(err, dataset) {
   dataset.get('myKey', function(err, value) {
    console.log(value, err);
   }); 
  });
 });
}

The AWS Credentials for the Identity Pool and the Facebook Token are previously set, and work in the online mode, but I don't get the dataset data, when being online.

Am I doing something wrong or is it generally not possible to get the Cognito Dataset data while being offline? I read, that the data is actually being held in the local storage.

I am using the current AWS SKD (Release v2.1.42) and the Amazon Cognito JS.