Immutable data.

Any operation that would mutate a data structure in Immutable.js does not modify the original value.

But rather returns a new value.

Iterable

An Iterable is a set of key/value entries that can be iterated (e.g. using .map(), .filter(), .reduce(), …)

All collections in Immutable.js, like Map and List, use Iterable as a base class.

Maps

Think of Map as an object.

.fromJS() This returns a given JS object as an Immutable.js representation,

Converting objects into Maps, and arrays into Lists.