game.js

this.$table.addEventListener('click', function(event) {
  var state = store.getState();
  // [Prevent dispatch under certain conditions]
  // Otherwise, trigger `SET_X` or `SET_O`
  store.dispatch({
    type: state.turn === 'x' ? 'SET_X' : 'SET_O',
    index: parseInt(index, 10)
  });
});