text: /**
    * WeakSet are collection of objects. It allows to store weakly held objects 
    * in collection. Weakly held objects are unique across collection.
    * Unlike Set, WeakSet can only store Objects. Objects are held weakly and no
    * reference is stored and hence prevents leaking.
    */
  
  var x = {};
  var y = function(){};
  
  var ws = new WeakSet();
  
  ws.add(x);
  ws.add(y);
  
  ws.has(x); // true
  
  ws.delete(x);
  
  ws.clear(); // purge whole weakset
  