Redux MVP without npm install

App.tsx

// idea from https://medium.com/@dan_abramov/you-might-not-need-redux-be46360cf367
import './App.css';
import React, {useState} from "react";

interface ActionType {
    type: string;
}

function CounterReducer(state = {value: 0}, action: ActionType = {type: ""}) {
    switch (action.type) {
        case 'INCREMENT':
            return {value: state.value + 1}
        case 'DECREMENT':
            return {value: state.value - 1}
        default:
            return state
    }
}

function Counter() {
    const [state, setState] = useState(CounterReducer())

    function dispatch(action: ActionType) {
        setState(prevState => CounterReducer(prevState, action))
    }

    function increment() {
        dispatch({type: "INCREMENT"})
    }

    function decrement() {
        dispatch({type: "DECREMENT"})
    }

    return <div>
        {state.value}
        <button onClick={increment}>+</button>
        <button onClick={decrement}>-</button>
    </div>
}

function App() {
    return <Counter/>
}

export default App