loldux.js

function Atom(initialState) {
  this.state = initialState
  this.cbs = []
  this.on = (cb) => this.cbs.push(cb)

  this.swap = (f, a) => {
    this.state = f(this.state, a)
    this.cbs.forEach(cb => cb(this.state))
    return this.state
  }
  return this
}

const createStore = (reducer, initialState) => {
  const atom = new Atom(initialState)
  this.dispatch = action => atom.swap(reducer, action)
  this.on = f => {
    f(atom.state)
    atom.on(f)
  }
  return this
}


const root = (state, action) => {
  switch (action.type) {
    case "INC":
      state.counter++;
      return state;
    case "DEC":
      state.counter--;
      return state;
    default:
      return state
  }
}

const store = createStore(root, {counter: 0})

store.on(s => console.log("RENDER REACT TREE NOW WITH STATE:", s))

store.dispatch({type: "INC"})
store.dispatch({type: "INC"})
store.dispatch({type: "DEC"})