title: durandal.js viewmodel communication
body: <p>Does anyone know what's the easiest way to get an instance of a view model within another view model. To be more specific, i would like to load the instance of one view model into another view model so that the latter can call methods of the former.</p>
  
  <p>Does durandal keep a list of all view models that were used during the composition? </p>
  
  <p>I guess one way to deal with that is applying the pub/sub pattern which is supported by durandal. 
  Another way would probably be to manually get the view model with the aid of knockout and the dataFor utility function.
  However, i would like to know if there is a way to explicitly get the instance of a composed view model. </p>
  
  <p>Note: my modules expose a constructor rather that singleton object</p>