GameStore.js

let validActions = {
  [GameConstants.GAME_CREATE]: null,
  [GameConstants.GAME_JOIN]: null,
  [GameConstants.GAME_EXIT]: null,
  [GameConstants.USER_JOINED]: null,
  [GameConstants.USER_LEFT]: null
}

GameDispatcher.register( ({actionType, data}) => {
  if (actionType in validActions) {
    update(data)
    GameStore.emitChange()
  }
})

GameStoreAlt.js

// OR

let validActions = [
  GameConstants.GAME_CREATE,
  GameConstants.GAME_JOIN,
  GameConstants.GAME_EXIT,
  GameConstants.USER_JOINED,
  GameConstants.USER_LEFT
]

GameDispatcher.register( ({actionType, data}) => {
  if (validActions.contains(actionType)) {
    update(data)
    GameStore.emitChange()
  }
})