TypeScript

Reducer

出典: Typescript×ReduxでStateがundefinedに？確認すること！ — ソースコードを解説 / Reducer

Reducer (typescript)#c6a3f4c3b4fc

import {ActionNames, ActionType} from "../Actions/CounterAction";
 
 
export interface IState {
	num : number
}
 
const initialState : IState = {num: 0};
 
const CounterReducer = (state : IState = initialState , action : ActionType): IState => {
	switch (action.type) {
		case ActionNames.Increment:
			return {num : state.num + 1};
		case ActionNames.Decrement:
			return {num : state.num - 1};
		default:
			return state;
	}
};
 
export default CounterReducer;

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id: #c6a3f4c3b4fc
lines: 21
extracted: 2026-06-10

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この snippet は記事の「ソースコードを解説 / Reducer」セクションに登場する。コードの前後の文脈・ハマりどころの解説は記事本文で。

技術記事Gitデータ有React

Typescript×ReduxでStateがundefinedに？確認すること！

6年前12 min

同じ記事から

11 件

TypeScript

import {Action} from 'redux'

export enum	ActionNames{
	Increment = 'inc',

未収録

Action

#f6e047b97c21

TypeScript

import {combineReducers,createStore,Action} from 'redux'
import CounterReducer, {IState} from "../Reducers/CounterReducer";
import {ActionType} from "../Actions/CounterAction";

未収録

Store

#3016f3544502

TypeScript

import {ReduxAction, ReduxState} from "../Store/store";
import {DecrementAmount, IncrementAmount} from "../Actions/CounterAction";
import {connect} from "react-redux";
import {Dispatch} from "react";

未収録

Container

#adc8bd5d5619

TypeScript

import React from "react";
import {IState} from "../Reducers/CounterReducer";
import {ActionDispather} from "./Container";

未収録

Component

#cef49ac152ba

TypeScript

import React from 'react';
import ReactDOM from 'react-dom';
import * as serviceWorker from './serviceWorker';
import {Provider} from "react-redux";

未収録

Index

#137a571c0501

TypeScript

	render() {
		return (
			<div>
				{/*<p>CurrentCount:{this.props.value.num}</p>*/}

▶ 実行可

Reduxでstateが undefinedに？どんな現象？

#724b87f56936

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