var subscribed = new ReactiveVar(false); // Going off memory, i think its like that

getMeteorData() {
  let subscribed = subscribed.get(); // Important to call get so that getMeteorData continues to watch this.
  return { subscribed }; // Same as { subscribed: subscribed } in babel compiler.
}

sub() {
  subscribed.set(true);
}

render() {
  return (<div onClick={this.sub}>{ this.data.subscribed ? 'Subscribed' : 'Click here to subscribed' }</div>);
}