javascript nested class

how i interpretation nested category java script.

here formula dash i have:

obja = new testa();

function testb ()
{
   this.testprint = duty ()
  {
     imitation ( " inside testprint " );
  }
}

function testa ()
{
   var myobjb = new testb();
}

now i am perplexing opening testprint controlling obja

obja.myobjb.testprint();

but the giving blunder "obja properties"

how i opening testb slight controlling obja handler?