code: function forIn(object, fn, scope) {
      var symbols,
          k,
          i,
          l;
  
      for (k in object)
        fn.call(scope || null, k, object[k]);
  
      if (Object.getOwnPropertySymbols) {
        symbols = Object.getOwnPropertySymbols(object);
  
        for (i = 0, l = symbols.length; i < l; i++)
          fn.call(scope || null, symbols[i], object[symbols[i]]);
      }
    }
docs: Iterate over an object that may have ES6 Symbols.
  
  @param  {object}   object  Object on which to iterate.
  @param  {function} fn      Iterator function.
  @param  {object}   [scope] Optional scope.