Notice the number and order of the output.

DataSource Listening

function run_demo() {
  var k = new goog.ds.JsDataSource([], 'mypath');

  goog.ds.DataManager.getInstance().addListener(function (a,b) {console.log(a,b);}, k.getDataPath() + '/fi');

  k.setChildNode('fee', {'data': 1});
  k.setChildNode('fi', {'data': 2});
  k.setChildNode('fo', {'data': 3});
  k.setChildNode('fum', {'data': 4});
  
}

>mypath
>mypath/fi
>mypath
>mypath
>mypath