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Koutaro Chikuba
Koutaro Chikuba

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Minimum flux with useReducer

Inject state and dispatcher context by React.Context and useContext

import React, { useReducer, useContext, Dispatch, ReactElement } from "react";
import ReactDOM from "react-dom";

type CounterState = {
  count: number;

const initialState: CounterState = { count: 0 };

function reducer(state: CounterState, action: any) {
  switch (action.type) {
    case "reset": {
      return initialState;
    case "increment": {
      return { count: state.count + 1 };
    case "decrement": {
      return { count: state.count - 1 };
    default: {
      return state;

// Container
const CounterContext = React.createContext<CounterState>(null as any);
const DispatchContext = React.createContext<Dispatch<any>>(null as any);

function App({ initialCount }: { initialCount: number }) {
  const [state, dispatch] = useReducer(reducer, { count: initialCount });
  return (
    <CounterContext.Provider value={state}>
      <DispatchContext.Provider value={dispatch}>
        <Counter />

// Connected component
function Counter() {
  const state = useContext(CounterContext);
  const dispatch = useContext(DispatchContext);
  return (
      Count: {state.count}
      <button onClick={() => dispatch({ type: "reset" })}>Reset</button>
      <button onClick={() => dispatch({ type: "increment" })}>+</button>
      <button onClick={() => dispatch({ type: "decrement" })}>-</button>

ReactDOM.render(<App initialCount={2} />, document.querySelector(".root"));

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