Most efficient way to get all sub sites under a site collection/sub site using JSOM?

For the question lets assume the following site hierarchy

• Root Site
  
  
  
  • Sub Site 01
    
    
    
    • Sub Site 0101
    
    
    • Sub Site 0102
      
      
      
      • Sub Site 010201
      
      
      
      
    
    
    
    
  
  
  • Sub Site 02
  
  
  • Sub Site 03
    
    
    
    • Sub Site 0301
    
    
    
    
  
  
  
  

Now if I want to get all these sub site object in an array, what would be the best approach.

PS - rootWeb.get_webs() would return me just the immediate child sub sites. This would require me the make a recursive async call to each child sub site to get further down the hierarchy. I m guessing this will have performance issues and callback challenges.