// At top, import immutable
import { Map } from 'immutable';

// Later, in constructor...
this.state = {
  // Create an immutable map in state using immutable.js
  user: Map({ firstName: 'Cory', lastName: 'House'})
};

updateState({target}) {
 // this line returns a new user object assuming an immutable map is stored in state.
 let user = this.state.user.set(target.name, target.value);
 this.setState({user});
}