text: // weak maps and sets.js
  
  (function(){
      'use strict';
      let myWeakSet = new WeakSet();
  
      let someobj = {};
      myWeakSet.add(someobj);
      console.log(myWeakSet.has(someobj)); // will return true
  
      myWeakSet.delete(someobj);
      console.log(myWeakSet.has(someobj)); // will return false because it already deleted
  
      let myWeakMap = new WeakMap();
  })();