redux-without-redux

class Observable {
  constructor(value) {
    this.value = value
    this.events = { change: [] }
  }
  
  update(updateFn) {
    this.value = updateFn(this.value)
    this.events.change.forEach(fn => fn(this.value))
  }
  
  onChange(fn) {
    this.events.change.push(fn)
  }
}

class Store extends Observable {
  constructor(reducer) {
    super(reducer())
    this.reducer = reducer
  }
  
  dispatch(action) {
    this.update(state => this.reducer(state, action))
  }
}

class Connect {
  constructor(props) {
    this.props = props
    this.state = props.store.value
    
    this.props.store.onChange(storeState => {
      this.state = storeState
      this.render()
    })
  }
  
  render() {
    const Component = this.props.component
    return new Component(this.props.mapStateToProps(this.state)).render()
  }
}

const Provider = store => component => props => 
  new component({ ...props, store })

const connect = mapStateToProps => component => props => 
  new Connect({ ...props, component, mapStateToProps })

// app code

const actionTypes = {
  INC: 'INC',
  DEC: 'DEC'
}

const actions = {
  inc: () => ({ type: actionTypes.INC }),
  dec: () => ({ type: actionTypes.DEC })
}

const initialState = { timeElapsed: 0 }

const rootReducer = (state = initialState, action = {}) => {
  switch(action.type) {
    case actionTypes.INC:
      return ({ timeElapsed: state.timeElapsed + 1 })
    
    case actionTypes.DEC:
      return ({ timeElapsed: state.timeElapsed - 1 })
    
    default:
      return state
  }
}

const store = new Store(rootReducer)
 
class App {
  constructor(props) {
    this.props = props
  }
  
  render() {
    const template = `time elapsed: ${this.props.timeElapsed} seconds`
    document.getElementById('app').innerHTML = template
  }
}

const connected = connect(x => x)(App)

const ProvidedApp = Provider(store)(connected)

const app = new ProvidedApp()

app.render()

const incrementTimer = () => store.dispatch(actions.inc())
const decrementTimer = () => store.dispatch(actions.dec())

setInterval(incrementTimer, 1000)
setInterval(decrementTimer, 5000)