Redux reducer todolist Immutable equivalent

Question

I'm trying to rewrite the redux todo example in immutable.js, so far I've just made the initalstate an immutable list and changed the add to and unshift rather than a spread operator, it seems to be working fine. form the immutable docs it seem to say you can use all these unshift , push etc.. on a list, so i think this might be ok?.

i've seen some examples where instead of .List() they used .fromJS() also wrapping the object that's being push / unshift etc in .fromJS()

so, my question

is this all that's required to make it immutable ?

const initialState = Immutable.List([{
  text: 'Use Redux',
  marked: false,
  id: 0
}]);

export default function todos(state = initialState, action) {
  switch (action.type) {

    case ADD_TODO:
    return state.unshift({
      id: state.reduce((maxId, todo) => Math.max(todo.id, maxId), -1) + 1,
      completed: false,
      text: action.text
    });

    case DELETE_TODO:
      return state.filter(todo =>
        todo.id !== action.id
      )

    case EDIT_TODO:
      return state.map(todo =>
        todo.id === action.id ?
          Object.assign({}, todo, { text: action.text }) :
          todo
      )

    case COMPLETE_TODO:
      return state.map(todo =>
        todo.id === action.id ?
          Object.assign({}, todo, { completed: !todo.completed }) :
          todo
      )

    case COMPLETE_ALL:
      const areAllMarked = state.every(todo => todo.completed)
      return state.map(todo => Object.assign({}, todo, {
        completed: !areAllMarked
      }))

    case CLEAR_COMPLETED:
      return state.filter(todo => todo.completed === false)

    default:
      return state
  }
}