How to use useReducer and useContext hooks together with Typescript in React

Introduction

Are your components complex with too many states and props?. It is time to use UseReducer and UseContext hooks now to simplify them and keep them clean.

In this article, we will see how to use useReducer and useContext hooks together with typescript in a step-by-step guide. If you are not familiar with useReducer and useContext, have read through in ReactJS site

What is useReducer?. https://reactjs.org/docs/hooks-reference.html#usereducer

What is useContext?. https://reactjs.org/docs/hooks-reference.html#usecontext

To showcase the use of useReducer and useContext hooks, we will create a simple poker game app in React and manage the game state using useReducer/useContext hooks. Let’s get started. Note: All the code sample mentioned below can be found in the github repo [here] (https://github.com/hellomuthu23/react-context-example)

Steps

npx create-react-app react-context-app --template typescript
# or
yarn create react-app react-context-app --template typescript

Navigate to react-context-app and run yarn start command to start the app. Access the app http://localhost:3000.

While adding new files follow the below folder structure, and refer to the Github repo if you need any information on the imports, css files — https://github.com/hellomuthu23/react-context-example

2. Add State: Let’s create a GameState that will hold the game state, the state will have players, gameName, winner details, and game status.

export interface GameState {
players: Player[];
gameName: string;
winner: Player | null;
gameStatus: Status;
}

export enum Status {
NotStarted = 'Not Started',
InProgress = 'In Progress',
Finished = 'Finished',
}

export interface Player {
name: string;
id: number;
status: Status;
value?: number;
}

export const initialGameState: GameState = {
players: [],
gameName: 'Game1',
winner: null,
gameStatus: Status.NotStarted,
};

3. Add Actions: Now let’s add required Actions types for the poker games, actions like adding a player to the game, resetting the game, and playing the game.

export enum ActionType {
AddPlayer,
SetPlayerValue,
ResetGame,
}

export interface AddPlayer {
type: ActionType.AddPlayer;
payload: Player;
}

export interface SetPlayerValue {
type: ActionType.SetPlayerValue;
payload: { id: number; value: number };
}

export interface ResetGame {
type: ActionType.ResetGame;
}

export type GameActions = AddPlayer | SetPlayerValue | ResetGame;

4. Add Reducer: Let’s add a reducer file that will update the state for specific/required actions and side effects(calculate winner, game status, etc).

export function gameReducer(state: GameState, action: GameActions): GameState {
switch (action.type) {
case ActionType.AddPlayer:
return { ...state, players: [action.payload, ...state.players] };
case ActionType.ResetGame:
return {
...initialGameState,
players: state.players.map((player) => ({
...player,
status: Status.NotStarted,
value: 0,
})),
};
case ActionType.SetPlayerValue:
let newState = {
...state,
players: state.players.map((player: Player) =>
player.id === action.payload.id
? {
...player,
value: action.payload.value,
status: Status.Finished,
}
: player
),
};

return {
...newState,
winner: getWinner(newState.players),
gameStatus: getGameStatus(newState),
};

default:
return state;
}
}

const getWinner = (players: Player[]): Player | null => {
let winnerValue = 0;
let winner = null;
players.forEach((player) => {
if (player.value && player.value > winnerValue) {
winner = player;
winnerValue = player.value || 0;
}
});
return winner;
};

const getGameStatus = (state: GameState): Status => {
const totalPlayers = state.players.length;
let numberOfPlayersPlayed = 0;
state.players.forEach((player) => {
if (player.status === Status.Finished) {
numberOfPlayersPlayed++;
}
});
if (numberOfPlayersPlayed === 0) {
return Status.NotStarted;
}
if (totalPlayers === numberOfPlayersPlayed) {
return Status.Finished;
}
return Status.InProgress;
};

// helper functions to simplify the caller
export const addPlayer = (player: Player): AddPlayer => ({
type: ActionType.AddPlayer,
payload: player,
});

export const setPlayerValue = (id: number, value: number): SetPlayerValue => ({
type: ActionType.SetPlayerValue,
payload: { id, value },
});

export const resetGame = (): ResetGame => ({
type: ActionType.ResetGame,
});

5. Add Context: Now let’s add a context file

Create context.ts with below GameContext that uses the above-created State. We will use this context using useContext hook in the components.

export const GameContext = React.createContext<{
state: GameState;
dispatch: React.Dispatch<GameActions>;
}>({
state: initialGameState,
dispatch: () => undefined,
});

6. Add useContext and useReducer hook to the App: Now that we have created the necessary context, state, etc, we can add them into the app.

export const Poker = () => {
const [state, dispatch] = useReducer(gameReducer, initialGameState);
return (
<GameContext.Provider value={{ state, dispatch }}>
<div className='Header'>
<header>
<p>React useReducer and useContext example Poker App</p>
</header>
</div>
<div className='ContentArea'>
<div className='LeftPanel'>
<PlayersList />
</div>
<div className='MainContentArea'>
<Players />
</div>
<div className='RightPanel'>
<GameStatus />
</div>
</div>
<div className='Footer'>
<AddPlayer />
</div>
</GameContext.Provider>
);
};

Add the <Poker/> component to App.tsx component file.

7. Add Components: It’s time to add the components and play the game.

export const AddPlayer = () => {
const { dispatch } = useContext(GameContext);

const [playerName, setPlayerName] = useState('');

const handlePlayerNameChange = (event: ChangeEvent<HTMLInputElement>) => {
setPlayerName(event.target.value);
};

const handleSubmit = (event: FormEvent) => {
const player: Player = {
id: +new Date(),
name: playerName,
status: Status.NotStarted,
};
dispatch(addPlayer(player));
setPlayerName('');
event.preventDefault();
};
return (
<>
<h4>Add New Player</h4>
<form onSubmit={handleSubmit}>
<input
value={playerName}
type='text'
onChange={handlePlayerNameChange}
/>
<button type='submit' value='Submit' disabled={playerName === ''}>
Add
</button>
</form>
</>
);
};
export const PlayersList = () => {
const { state } = useContext(GameContext);
return (
<div className='PlayersList'>
<h4>Players</h4>
{state.players.map((player) => (
<label>{player.name}</label>
))}
</div>
);
};
export const Players = () => {
const { state, dispatch } = useContext(GameContext);
const playPlayer = (id: number) => {
const randomValue = Math.floor(Math.random() * 100);
dispatch(setPlayerValue(id, randomValue));
};
return (
<div>
<h4>Players Status</h4>
<div className='PlayersContainer'>
{state.players.map((player: Player) => (
<div key={player.id} className='Player'>
<label>Name: {player.name}</label>
<label>Status : {player.status}</label>
<label>Card Value: {player.value}</label>
<button
disabled={player.status !== Status.NotStarted}
onClick={() => playPlayer(player.id)}
>
Show Card
</button>
</div>
))}
</div>
</div>
);
};
export const GameStatus = () => {
const { state, dispatch } = useContext(GameContext);
return (
<div className='GameStatus'>
<div className='Status'>
<h4>Game Status</h4>
<label>{state.gameStatus}</label>
<button onClick={() => dispatch(resetGame())}>Start New Game</button>
</div>
<div className='Winner'>
{state.gameStatus === Status.InProgress && (
<label>
In Lead : {state.winner?.name} by {state.winner?.value}
</label>
)}
{state.gameStatus === Status.Finished && (
<label>
Winner: {state.winner?.name} by {state.winner?.value}
</label>
)}
</div>
</div>
);
};

Add CSS file: copy the required CSS files from the Github repo here: https://github.com/hellomuthu23/react-context-example

Play the Game: Once you have added all necessary components, CSS, and states, you should be ready to play the game and see the use of useContext and useReducer hooks in action.

Game screenshot

Conclusion

Hope you had fun creating useContext and useReducer hooks and playing the game. As you have seen, the components look a lot clean without too many props/state and easy to manage the state/actions using useContext hook.

Full working demo: https://codesandbox.io/s/quirky-grass-4f0yf?fontsize=14&hidenavigation=1&theme=dark

Github repo: https://github.com/hellomuthu23/react-context-example

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store