code: function getIteratorFn(maybeIterable) {
    var iteratorFn = maybeIterable && (
      (ITERATOR_SYMBOL && maybeIterable[ITERATOR_SYMBOL]) ||
      maybeIterable[FAUX_ITERATOR_SYMBOL]
    );
    if (typeof iteratorFn === 'function') {
      return iteratorFn;
    }
  }
docs: Before Symbol spec. 
  Returns the iterator method function contained on the iterable object.
  
  Be sure to invoke the function with the iterable as context:
  
  var iteratorFn = getIteratorFn(myIterable);
  if (iteratorFn) {
  var iterator = iteratorFn.call(myIterable);
  ...
  }
  
  @param {?object} maybeIterable
  @return {?function}