title: Why Rx.Observable.of(true) starts to emit
body: <p>I have following code:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>console.log('start');
  
  //emit value every second
  const message = Rx.Observable.interval(1000);
  //emit value as soon as subscribed
  const trueObs = () =&gt; Rx.Observable.of(true);
  // start emitting delayed values as soon as trueObs emits
  const delayWhenExample = message.delayWhen(trueObs);
  //log values start logging after one second
  //ex. output: 0...1...2...3
  const subscribe = delayWhenExample.subscribe(val =&gt; console.log(val));</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;script src="https://npmcdn.com/@reactivex/rxjs@5.0.0-beta.8/dist/global/Rx.umd.js"&gt;&lt;/script&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>Why <code>Rx.Observable.of(true)</code> starts to emit value without <code>subscribe</code> the observable?<br>
  I understand the concept to RxJS as lazy evaluation, it does not emit values, until I am asking it.</p>