title: rxjs - is there something like an wait until first Operator?
body: <p>I have two observables <code>one$</code> and <code>two$</code>;</p>
  
  <p>I want <code>one$</code> only to fire when two$ has been fired at least once. This I think is essentially the <code>skipUntil</code> operator.</p>
  
  <pre><code>one$.skipUntil(two$).subscribe()
  </code></pre>
  
  <p>But let's say <code>one$</code> has fired while <code>two$</code> hasn't. I want a behaviour where the stream remembers that <code>one$</code> has fired and will fire at least once, as soon as <code>two$</code> did.</p>
  
  <p>Cheers</p>