Ionic native map

I’m trying to use the ionic Native Map in my App.
here is my code:
`this.platform.ready().then(() => { = new GoogleMap(‘article-details-map’);

  GoogleMap.isAvailable().then(() => { =>{
      console.log('Map is ready!');
      alert("GoogleMap.onMapReady(): " + JSON.stringify(data));


I have test the code on a real device and with the Chrome inspector i get this error

EXCEPTION: Error: Uncaught (in promise): TypeError:…).subscribe is not a function

it’s on() instead of one()