I am using the following code(picked from facebook's immutable.js page): 

```
    Immutable.Seq({a:1, b:1, c:1})
  .flip().map(key => key.toUpperCase()).flip().toObject();

```

I am trying to find where the flip() function is defined. 
 Checking the properties of Seq object and then after applying flip() to Seq object, it returns:

```
Seq [ '_object', '_keys', 'size' ]

Seq flip [ '_iter',
  'size',
  'flip',
  'reverse',
  'has',
  'includes',
  'cacheResult',
  '__iterateUncached',
  '__iteratorUncached' ]

```

I am guessing it is a part of the immutable library. lodash has a similar function but it's not the same.

Vikram