$(document).ready(function(){

  var currentPlayer = $("#table").data("current-player");

  $(".square").click(function(){
    //   Gather the position that was clicked
    var number = $(this).data("position");
    // Locate the game form
    var form = $("form");
    // Locate the input field corresponding to that position
    var input = $("input[data-position='" + number + "']");
    // Set the value of that input field to "X" or "O"
    input.val(currentPlayer);
    // Submit the form
    form.submit();
  });
});

def update
  @game = Game.find(params[:id])
  @game.update(game_params)
  redirect_to @game
  switch_player
end

def switch_player
  session[:current_player] = session[:current_player] == 'X' ? 'O' : 'X'
end

<%= nested_form_for @game do |f| %>

  <%= f.fields_for :moves do |move_form| %>
    <p id="table" data-current-player: <%=session[:current_player] %>>
      <%= move_form.label :position %><br>
      <%= move_form.text_field :player, data: {position: move_form.object.position} %>
      <%= move_form.hidden_field :id %>
    </p>
  <% end %>

<input type="Submit">
<% end %>

<div id="board" align = center>
  <table>
    <tr>
      <td data-position="0" class="square <%= class_for_move(0)%>"></td>

def class_for_move(number)
  move = @game.moves.find_by(position: number)
  player = move.player
  player.downcase + '_move' unless player.blank?
end