jQuery Tic-Tac-Toe with a Rails API — Part 2

Congratulations on setting up your Rails API back-end! Hopefully you took a short break to celebrate because the real fun starts now.

In this second installment, you're tasked with building out a JavaScript front-end to place on top of the Rails API we created in the previous exercise. For reference, here's the video showing how the final product should function. (Right-click and Save Link As... to download.)

Objectives

• Create a fully-functional tic-tac-toe game using jQuery and/or vanilla JavaScript.
• Make AJAX requests to a Rails API in order to save, update, and reload games.

Getting started

Code your solution in app/assets/javascripts/tictactoe.js, which we're loading via the Rails asset pipeline. As a refresher, we added that file to the asset pipeline by specifying //= require tictactoe in our JavaScript manifest file (app/assets/javascripts/application.js).

You are welcome to use jQuery, pure JavaScript, or a combination of the two, but you should not have to create any new files or modify anything outside of tictactoe.js.

Exploring the DOM

The only view our application requires lives in app/views/home/index.html. Before you dive into writing JavaScript, start the Rails server and familiarize yourself with the DOM that you'll be working with. Take special note of the way in which the squares of the game board are identified with data-x and data-y attributes.

Buttons!

button#save

Clicking this button should save the current game state. If the current game already exists in the database, saving it should update that previously-saved game. If the current game has not yet been persisted to the database, saving it should do so. As a brief example, if we start with a blank board that has not been saved and click button#save, the current game should be persisted to our database. If we then click button#save a second time, the persisted game should be updated (though, since we have yet to make any moves, the board will still be blank in the updated game state).

button#previous

Clicking this button should grab all of the persisted games from the database and create a button for each that, when clicked, returns that saved game's state to our tic-tac-toe board. All of the buttons should be added to the div#games element in the DOM.

button#clear

Clicking this button should clear the game board and start a completely new game. If we click button#save, then button#clear, and then button#save again, two games should have been persisted to the database.

Conjunction junction, what's your function?

For the actual TTT functionality, the test suite is pretty opinionated. We've given you a lot of the structure, and the tests force you down a pretty specific path as far as which functions you need to define and what they should do:

• player()
  • Returns the token of the player whose turn it is, 'X' when the turn variable is even and 'O' when it is odd.
• updateState()
  • Invokes player() and adds the returned string ('X' or 'O') to the clicked square on the game board.
• setMessage()
  • Accepts a string and adds it to the div#message element in the DOM.
• checkWinner()
  • Returns true if the current board contains any winning combinations (three X or O tokens in a row, vertically, horizontally, or diagonally). Otherwise, returns false.
  • If there is a winning combination on the board, checkWinner() should invoke setMessage(), passing in the appropriate string based on who won: 'Player X Won!' or 'Player O Won!'
• doTurn()
  • Increments the turn variable by 1.
  • Invokes the updateState() function, passing it the element that was clicked.
  • Invokes checkWinner() to determine whether the move results in a winning play.
• attachListeners()
  • Attaches the appropriate event listeners to the squares of the game board as well as for the button#save, button#previous, and button#clear elements.
  • When a user clicks on a square on the game board, the event listener should invoke doTurn() and pass it the element that was clicked.
  • NOTE: attachListeners() must be invoked inside either a $(document).ready() (jQuery) or a window.onload = () => {} (vanilla JavaScript). Otherwise, a number of the tests will fail (not to mention that your game probably won't function in the browser).
  • When you name your save and previous functions, make sure to call them something like saveGame() and previousGames(). If you call them save() and previous() you may run into problems with the test suite.

Testing

Note: Use var instead of let or const when defining variables in this lab. Due to compiler bugs, tests will fail to recognize working code.

You can run the test suite in one of two ways:

1. With Node (in your terminal) by running the learn or npm test command.
2. In the browser by opening up test/fixtures/index-test.html in your browser, opening the JS console, and invoking the mocha.run() method. Note that, on subsequent tests, you should refresh the page each time before invoking mocha.run().

Bonus(es)

1. Once all of the tests are passing and you have a functionally awesome / awesomely functional tic-tac-toe game with persistence, try refactoring your front-end to use ES6 classes and other OO design patterns. Think about the domain you're trying to model — how many classes do you need? What are the relationships between classes?
2. Implement a memoization scheme for minimizing the amount of database calls your application makes.
3. Modify the GameSerializer to include the updated_at attribute, and display the last-updated time next to each saved game in the DOM.

Resources

• jQuery data()

View jQuery Tic Tac Toe on Learn.co and start learning to code for free.