Immutable JS Integration

[keokilee]

There aren't any type definitions in DefinitelyTyped for this. There is a fork that has them, but since the developer hasn't provided tests, it's unlikely to get merged in soon.

https://github.com/umidbekkarimov/DefinitelyTyped/blob/b97976d391e42de9fbd341906120418c4b527900/immutable/immutable.d.ts

[Keats]

Immutablejs has definitions in its own repo: https://github.com/facebook/immutable-js/tree/master/type-definitions