react stateful function component

component.js

import React from 'react'
import {observer} from 'mobx-react'
import {observable} from 'mobx'

const state = observable({
  value: 0
})

const Comp = (props) => {
  return <div onClick={() => state.value++}>click to increase counter value: {state.value}</div>
}

export default observer(Comp)

Lovely reduction. Great starting point. You can really see where to go from here.