Flux-like IncrementStore as a Monoid

IncrementStore.js

const IncrementStore = state => ({
  state,
  concat: ({state: delta}) => {
    switch (delta.type) {
      case 'ADD':
        return IncrementStore({
          value: state.value + 1
        })

      case 'REMOVE':
        return IncrementStore({
          value: state.value - 1
        })

      default:
        return IncrementStore(state)
    }
  },
  fold: f => f(state)
})

IncrementStore.empty = () => IncrementStore({})

IncrementStore({value: 1}).concat(IncrementStore({type: 'ADD'}))