code: function WeakSet_constructor(iterable) { // @arg Iterator|Array = null
      this._value = [];
  
      var that = this;
  
      if (Array.isArray(iterable)) {
          iterable.forEach(function(value) {
              that["add"](value);
          });
      } else if (iterable && iterable["next"]) {
          var result = null;
  
          while ( (result = iterable["next"]()) ) {
              if (result["done"]) {
                  break;
              }
              this["add"](result["value"]);
          }
      }
  }
docs: === WeakSet ============================================