boardgame.io

Secret State

In some games you might need to hide information from players or spectators. For example, you might not want to reveal the hands of opponents in card games.

This is easily accomplished at the UI layer (by not rendering secret information), but the framework also provides support for not even sending such data to the client.

In order to do this, use the playerView setting in the game object. It accepts a function that receives an object containing G, ctx, and playerID, and returns a version of G that is stripped of any information that should be hidden from that specific player.

const game = {
  // `playerID` could also be null or undefined for spectators.
  playerView: ({ G, ctx, playerID }) => {
    return StripSecrets(G, playerID);
  },
  // ...
};

!> Make sure that you associate the game clients with individual players (as discussed in the Multiplayer section).

PlayerView.STRIP_SECRETS

The framework comes bundled with an implementation of playerView that does the following:

• It removes a key named secret from G.
• If G contains a players object, it removes all keys except for the one that matches playerID.

G: {
  secret: { ... },

  players: {
    '0': { ... },
    '1': { ... },
    '2': { ... },
  }
}

becomes the following for player 1:

G: {
  players: {
    '1': { ... },
  }
}

Usage:

import { PlayerView } from 'boardgame.io/core';

const game = {
  // ...
  playerView: PlayerView.STRIP_SECRETS,
};

Disabling moves that manipulate secret state on the client

Moves that manipulate secret state often cannot run on the client because the client doesn’t have all the necessary data to process such moves. These can be marked as server-only by setting client: false on move:

moves: {
  moveThatUsesSecret: {
    move: ({ G, random }) => {
      G.secret.value = random.Number();
    },

    client: false,
  }
}

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