title: Use Observables to handle caching API calls
body: <p>I would like to set up a cache by having a service hold a reference to a <code>BehaviorSubject</code> which will call an API endpoint initially and then emit that result. The tricky thing for me is figuring out how to set a TTL so that if XX seconds has elapsed it recalls the API endpoint instead of returning the last result.</p>
  
  <p>Is this possible with RxJS, or would I need to set up my own timers to 'reset' the <code>BehaviorSubject</code>?</p>