Before you initialize the SDK you will want to add a change event listener to get notified when the internal state of the field’s change. 
const myListener = (changeEvent) => {
  console.log(`Change Type: `, changeEvent.type);
  console.log(`Current State: `, changeEvent.state);
  updateMyUi(changeEvent.state);
};

window.confidoHostedFields.addChangeListener(myListener);
For a full list of Change Event types and a complete description of the state object, see the Hosted Fields SDK Reference Docs