gistfile1.js

// immutable object assignment:
const initialState = { products: {} };
export default function reducer(state = initialState, action = {}) {
  switch (action.type) {
    case PUT_PRODUCT:
      return { ...state, products: { ...state.products, [action.product.id]: action.product } };
    default:
      return state;
  }
}

// immutable array insertion:
// action.number (number to insert), action.index (array index to insert at)
const initialState = { numbers: [] };
export default function reducer(state = initialState, action = {}) {
  switch (action.type) {
    case PUT_NUMBER:
      return { ...state, numbers: [ ...state.numbers.slice(0, action.index),
                                    action.number,
                                    ...state.numbers.slice(action.index + 1) ] };
    default:
      return state;
  }
}