Type-checking Redux State with propTypes (without React)

TodoReducer.js

import withPropTypes from 'withPropTypes.js'

const ItemSchema = {
    id: propTypes.number,
    done: propTypes.bool.isRequired,
    title: propTypes.string.isRequired,
}

const TodoReducerSchema = propTypes.arrayOf(
    propTypes.shape(ItemSchema).isRequired
).isRequired

let id = 0

const TodoReducer = (state = [], action) => {
    switch (action.type) {
        case 'ADD_TODO':
            return [...state, {
                id: ++id,
                title: action.payload.title,
                done: action.payload.done,
            }]
        default:
            return state
    }
}

export default withPropTypes(
    'TodoReducer',
    TodoReducerSchema,
)(TodoReducer)