title: How to create knockout observable subscription that fires only once?
body: <p>In my model I have a property that is loaded asynchronously. I want it to generate another model property after it loads.</p>
  
  <p>I was thinking about subscription that could fire after the 1st property changes, generates the 2nd property and then get disposed - I don't know how can I dispose subscription from inside itself. </p>
  
  <p>Is there a way to fire one time event after observable property changes?</p>