TypeScript + Reduxはもうぼちぼちサードライブラリに頼らなくてもある程度はいい感じに補完してくれる

import {
  createStore,
  Reducer,
  Action,
  combineReducers,
  ActionCreatorsMapObject,
  ReducersMapObject,
  ActionCreator
} from "redux"

//// State全体の定義
export type AppState = {
  counter: number
}

//// ActionとActionCreatorの定義
// type CounterAction = Action<"INCREMENT" | "DECREMENT"> でも可
type CounterActionType = "INCREMENT" | "DECREMENT"
type CounterAction = Action<CounterActionType>

// これだけだるいが利用側のために二重定義してる。後述
export interface CounterActionCreators
  extends ActionCreatorsMapObject<CounterAction> {
  increment: ActionCreator<CounterAction>
  decrement: ActionCreator<CounterAction>
}
export const counterActions: CounterActionCreators = {
  increment: () => {
    return { type: "INCREMENT" }
  },
  decrement: () => {
    return { type: "DECREMENT" }
  }
}

//// Reducer。genericsらへんはちょっと怠けてる
const counterReducer: Reducer = (state = 0, action: CounterAction) => {
  switch (action.type) {
    case "INCREMENT": // このへんVSCode補完効いて最高の気分
      return state + 1
    case "DECREMENT":
      return state - 1
  }
  return state
}

export const generateStore = () => {
  const reducerMap: ReducersMapObject<AppState> = {
    counter: counterReducer
  }
  return createStore(combineReducers(reducerMap))
}

// Counter sample
import React, { Component } from "react"
import { connect } from "react-redux"
import { bindActionCreators, Dispatch } from "redux"
import {
  counterActions,
  AppState,
  CounterActionCreators
} from "../store"

// State -> Propsに変換する例。
// 変換不要なら type StateProps = AppState でいいだろう
type StateProps = {
  cnt: number
}
// 子のPropsはStatePropsとCounterActionCreatorsを持つ
type ChildProps = StateProps & CounterActionCreators

class CounterInner extends Component<ChildProps> {
  render() {
    return (
      <div>
        <div>{this.props.cnt}</div>
        <button onClick={this.props.increment}>+</button>
        <button onClick={this.props.decrement}>-</button>
      </div>
    )
  }
}

const connectCounter = connect(
  (state: AppState): StateProps => ({
    cnt: state.counter
  }),
  (dispatch: Dispatch) => bindActionCreators(counterActions, dispatch)
)
export const Counter = connectCounter(CounterInner)