title: Function synchronization and observable
body: <p>I have a Typescript function which converts a list of elements into a Map: Map.</p>
  
  <p>Along this process of conversion, I need to modify something in the Map before returning the Map.
  To obtain the info, I have to request a server so I have a http.GET request/subscription to get the value.</p>
  
  <p>I am using the value right after the GET, and the server has not yet answer, so I am returning the Map with the wrong value.
  (It comes later but too late).</p>
  
  <p>Then I use this map in which I don't have the correct value</p>
  
  <p>I need a mechanism to synchronize my function with the result of my GET request, before processing the Map later in my code (after returning the function).</p>
  
  <p>How can I do this, I have been told that the Observable may be the solution, but I don't know how to do it.</p>
  
  <p>I could use some help ;-).</p>
  
  <p>Best regards,
  Charles.</p>