Learn how to build a grid with CSS Grid and manage complex state with useReducer while building a Tic Tac Toe Game.

Kyle Shevlin

Manage Complex Tic Tac Toe Game State in React

Learn how to implement data structures, sorting algorithms, and the trade-offs between what algorithms to choose.

Data Structures and Algorithms in JavaScript

Managing state is one of the primary reasons our applications become so complex. See how to simplify state with state machines.

Introduction to State Machines Using XState

Functional Programming can be overwhelming to learn with all the new jargon and concepts. Learn this style without all the headaches.

Just Enough Functional Programming in JavaScript

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 Courses from Kyle Shevlin

JavaScript® (often shortened to JS) is a lightweight, interpreted, object-oriented language with first-class functions, most known as the scripting language for Web pages, but used in many non-browser environments as well such as node.js or Apache CouchDB. It is a prototype-based, multi-paradigm scripting language that is dynamic, and supports object-oriented, imperative, and functional programming styles.

javascript

We should add some final touches to our tic-tac-toe game. We want to make sure that after a user has won, that it's impossible for them to put the game into a broken state. We can do that by adding a guard to our `reducer`.

It would also be nice if the board automatically reset in the result of a draw. We can add a `checkForDraw` function that algorithmically determines if the game is drawn or not and automatically reset the `grid` data.

Prevent Impossible States and Check for Draw Conditions with Guard Statements in React

Tic-tac-toe, like many grid-based games, relies upon a 2-dimensional array data structure to hold the state of our `grid`.

A `grid` is a matrix. The outer array contains all the `rows`, and each row is an array of `columns`. Often each column value is referred to as a `cell`. In tic-tac-toe, we create a 3x3 grid of `null` values that will be replaced with `X`s and `O`s as the user interacts with the game.

Create a 2-Dimensional Grid for our Tic-Tac-Toe Game

React is one of the web’s most popular frameworks for building JavaScript applications. 

If you know what you’re doing, React can drastically simplify how you build, use, and maintain code.

Whether you’re a React newbie or you’re ready for advanced techniques, you can level-up with egghead. Explore our in-depth courses, lessons, and community resources to build more powerful applications and crack open your career.

react

Our tic-tac-toe board works and can be played, but it can't be reset once the game is won or the board is full. Adding this is simple. We'll add another case to our `reducer` and use a function to regenerate the `initialState` of our game.

Reset React State with a Button and Function in our Tic-Tac-Toe Game

In order to update our UI when a user interacts with the buttons, we need to store and update the tic-tac-toe `grid` data somehow. We're going to use the `React.useReducer` hook to accomplish this.

With this hook, we are able to store some data (including our grid) and define `actions` that update that data. We'll work on adding a `CLICK` case to our `reducer` that will update the `grid` with either an `X` or an `O` according to whose `turn` it is.

Handle User Input by Adding State to the Tic-Tac-Toe Grid with React useReducer

A game a user can't interact with is hardly a game at all. We'll go through the process of turning our `Cell` components into accessible buttons and moving the click handling function up to our `Game` component where our state will eventually be handled.

Convert a 3x3 Tic-Tac-Toe Grid Interactive by Adding Buttons in React

Cascading Style Sheets bring order and beauty to our applications.

Our tic-tac-toe UI has to display our `grid` data. Using CSS Grid to do so is :chefs_kiss:. We'll create `Grid` and `Cell` components to handle our data. The `Grid` component will map our `rows` and `columns` and use the CSS Grid layout engine to correctly place them. We'll make our grid generically handle any amount of rows and columns we would throw at it. We'll use a simple trick with the `grid-gap` property to easily create the crossing lines of a tic-tac-toe game.

Map Over a 2-Dimensional Array to Create a Game Grid in React with CSS Grid

At this point, our game is fully usable. Users can add `X`s and `O`s and can see for themselves who has won or not. However, this is a computer game now and it should be programmed to determine who the winner is algorithmically.

Breaking down the problem of tic-tac-toe, one will realize that there are only 8 winning conditions in the game. We can create a handful of functions that will `checkForWin` when a square is clicked. Once we have determined the winner, we can update the UI to announce that to the users.

Check for Winning Conditions in React useReducer for Tic-Tac-Toe

Conditional logic can be very cumbersome and difficult to read. A single `if/else` block might be simple enough, but nesting several of them can lead to very complicated logic and difficult to read code.

Often, we can easily eliminate half of the branching through the use of guard statements and early returns. This lesson will take a function with a few nested `if/else` blocks and refactor it to remove all of the `else`s. The result will be simpler and, in my opinion, easier to read.

Remove Unnecessary `Else` Blocks with Guards and Early Returns

Attempting to render an object in a React component results in an error. Objects are not valid React elements, however, strings are. If we transform an object using `JSON.stringify()` into a string, we can render it just as we would any other string.

We can encapsulate this concern in a React component. We can then use this component in a React app wherever we might like to display an object on the screen. This is very useful for debugging purposes when `console.log` or a `debugger` are not your best options.

Render an Object with JSON.stringify in React

Statecharts are a formalism for modeling stateful, reactive systems. This is useful for declaratively describing the behavior of your application, from the individual components to the overall application logic.

xstate

Actions are "fire-and-forget" side effects that are triggered by transitions. We set functions on a transition object's `actions` property to have them called when a transition is taken.

```javascript
//...
EVENT_NAME: {
  target: 'name-of-state-to-transition-to',
  actions: [(context, event) => { sideEffectToFire(context, event) }]
}
//...
```

Add Actions to Transitions to Fire Side Effects

Actions aren't limited to being called on transitions. They can also be called when we enter or exit a state node. This is done through the `entry` and `exit` properties.

The API for `entry` and `exit` actions is the same as that for `actions` on transitions. It can receive a single function or an array of functions, each which will be called with the next `context` and the `event` object that caused the transition.

This is a powerful way to fire side effects based on states rather than transitions.

```javascript
//...
states: {
  broken: {
    entry: [
      (context, event) => {
        sideEffectToFireWhenWeEnterTheBrokenState(context, event)
      }
    ],
    exit: [
      (context, event) => {
        sideEffectToFireWhenWeExitTheBrokenState(context, event)
      }
    ]
  }
}
```

Trigger Actions When Entering and Exiting a XState State

As our state machines grow more complex, we might find ourselves in a situation where a state should only exist if the machine is already in another state. To do this, we can use hierarchical states.

Instead of attempting to define all the states of a machine at a top level, we can nest states that should only be available as children of a parent state. These substates are written _exactly_ like the states of the top level of a machine: with an `initial` property, and the `states` of the nested state graph.

Using hierarchical states is a great way to avoid needing to check for booleans in an application. If a state can only exist when another state exists, consider if the one isn't in fact a child of the other.

Simplify State Explosion in XState through Hierarchical States

Generally speaking, state machines do not and should not have a sense of _time_. They are intended to be pure functions that receive a state and event and return the next state. Pure functions by design have no sense of _history_.

Yet, it is occasionally useful to return to a previous state. How is this accomplished? With history state nodes. Each state object returned by XState contains a special property that points to the previous state. When a history state node is defined and is the target of a transition, the machine returns to this previously stored state.

We can create a history node by defining the `type` as `history`, and setting the `history` property to either `shallow` (the default) or `deep`.

Recall Previous States with XState History States Nodes

Unbeknownst to many, promises are state machines. They exist in either an `idle`, `pending`, `resolved` or `rejected` state. Because they can be modeled as state machines, we can invoke them when we enter a state in a `Machine`.

We invoke services such as a promise by using the `invoke` property on a state node. When the state is entered, the `src` of the `invoke` object is called. In the case of promises, the `Promise` is called. When the `Promise` resolves, the `onDone` transition is taken. When the `Promise` rejects, the `onError` transition is taken. In either case, the data returned from the promise, whether resolved or errored, is passed back on the event object as `event.data`.

Invoking a Promise for Asynchronous State Transitions in XState

We can invoke a callback as a service when we enter a state in XState. This gives us the ability to trigger various functionality by responding to events sent to the service, and allows us to send events _back_ to the parent machine.

We do this by writing a "callback handler" and setting it as the `src` of our invoked service. A callback handler is a function that receives the current `context` and the `event` object that triggered the invocation. This function returns another function that receives two functions as arguments. A `callback` function to send events to the parent machine, and an `onEvent` function for the handler to respond to events sent to the handler.

The way events are sent to the callback handler is by utilizing the `options` argument of the `send` action creator. We identify where we send events to using the `to` property, and setting the value to the `id` of our service.

Invoke Callbacks to Send and Receive Events from a Parent XState Machine

Trying to structure the state logic of an application as a single machine can begin to become unwieldy when we have too many states. It is often better to divide our app into smaller machines and invoke those machines as necessary.

When we enter a state in a machine, we can invoke a child machine. This machine can send and receive events from the parent. When the child machine reaches a final state, the `onDone` transition is taken by the parent's current state node.

To invoke a child machine, we use the `invoke` property and set the `src` property to a machine. We can forward events in the parent machine to the child machine by setting the property `autoForwards` to `true`. We can also send events to the child machine through setting the second argument of the `send()` function to `{ to: 'child-machine-id' }`.

The child machine can send events to the parent machine by using the `sendParent` function. In this way, parent and child machines can communicate.

Invoke Child XState Machines from a Parent Machine

Enumerating the possible states of a function is a sound way to write a function, but it is imperative and could benefit from abstraction. We can do this with a state machine.

A state machine formalizes how we enumerate states and transitions. For the sake of clarity and to emphasize the core concepts, I will be overly verbose with my code in this lesson.

In this lesson, we'll replace the state enum with individual state objects. We'll also replace our events `toggle()` and `break()` with events `TOGGLE` and `BREAK`. I'll also demonstrate the usefulness of the Machine's `initialState` getter and the `transition` method. Lastly, I'll show what happens when we pass erroneous states or events into our machine.

Replace Enumerated States with a State Machine

XState provides the `send` function to create an action that will send the event passed in to the machine. If we provide the second argument to the `send` function, the `options` object, we can send the event `to` a particular machine. This is useful when you have invoked a machine as a service on a state node, a concept that will be explored in a later lesson.

Send Events to the Machine with the XState Send Action Creator

It is considered best practice to use the string shorthand for actions, guards, and more when configuring an XState `Machine`. We do this by providing a second argument to the `Machine` factory function: the `options` object.

On this object, we can define our actions, guards, activities, services and more. We then refer to the name of these functions with a string of the same name.

```javascript
//...
broken: {
  entry: ['logBroken']
}
//...
// In the options object
{
  actions: {
    logBroken: (context, event) => { console.log('yo I am broke') }
  }
}
```

Replace Inline Functions with String Shorthands

It is often useful to identify conditional branching in your machine as a state itself. A state that is designed to determine the next state does not need a specific event sent to trigger the transition. Instead, we can use the "null event" to trigger an immediate, transient transition.

The null event is identified with an event name of an empty string `''`, and is immediately sent to the state upon entry. We can setup multiple targets with conditionals, or fire off actions to set up a future state with this transient transitions.

Use XState Null Events and Transient Transitions to Immediately Transition States

Transitions come in two varieties: "external" and "internal". By default, a transition is considered external. This means that a transition will _exit_ the current state node, and _enter_ the next state node (even if that state node is the state the machine is currently in). This exit/enter loop will trigger any actions that are set on the `exit` and `entry` properties.

A transition can be set to internal, either through setting a `.` (dot) in front of the state node name (as we do in this lesson), or through setting the property `internal` to `true` on the transition object.

When a transition is internal, it will not exit and enter the state node, which means that the actions in the `exit/transition/entry` loop will not be called.

Use Internal Transitions in XState to Avoid State Exit and Re-Entry

Stop waiting for a single AI agent! This lesson demonstrates a powerful workflow to massively parallelize your AI-driven development in Cursor. Learn how to use tools like `file-forge` to package your project context, prompt advanced AI models (like Gemini in AI Studio) to brainstorm features and generate setup scripts, and then leverage a custom `git worktree` CLI tool (`wt`) to automatically launch an "army" of isolated Cursor instances, each tackling a different task on its own branch.

**Workflow Demonstrated / Key Benefits:**

*   **Bundle Project Context:** Use `file-forge` to create an AI-friendly representation of your codebase.
*   **AI-Powered Brainstorming & Scripting:** Prompt a reasoning model (e.g., Gemini via AI Studio) to suggest features *and* generate a shell script (`zsh`/`bash`) to automate setup.
*   **Automated Worktree Creation:** Execute the generated script which uses a custom `git worktree` CLI (`wt`) to:
    *   Create new branches and worktrees for each suggested feature.
    *   Install dependencies automatically (e.g., `pnpm install`).
    *   Launch multiple, isolated Cursor instances.
*   **Parallel AI Development:** Assign different features or implementation approaches to each Cursor agent (Composer) simultaneously.
*   **Efficient Monitoring:** Easily switch between active Cursor projects/worktrees using `Ctrl+R` or OS spaces.
*   **Seamless Integration:** Merge completed features back into your main branch using `wt merge` or use agents to commit, push, and create Pull Requests via the GitHub CLI (`gh pr create`).
*   **Boost Productivity:** Dramatically speed up iteration and experimentation by running multiple AI agents concurrently without conflicts.

This approach transforms your workflow, allowing you to explore multiple development paths simultaneously and integrate the best results efficiently using standard Git practices.

**Resources** 

https://www.npmjs.com/package/@johnlindquist/worktree
https://www.npmjs.com/package/@johnlindquist/file-forge

**Want to Learn More? Sign-up for my Cursor Workshop!**

https://egghead.io/workshop/cursor

John Lindquist

Swarm Intelligence: Massively Parallelize Your AI Agents in Cursor

Creating powerful and context-aware tools for Cursor IDE becomes straightforward when leveraging information directly from your current project. In this lesson, you'll learn how to build a custom MCP (model context protocol) tool that intelligently requests essential details—such as the current project path and conversation summaries—from your Cursor project.

Workflow demonstrated in this lesson:

- Define MCP tool parameters to request specific project details.
- Pass project path and conversation summaries into your MCP tool.
- Automatically write or update files within your current project using these parameters.

Key benefits:

- Automate tasks with precision based on your active project's context.
- Simplify interactions by creating AI-driven CLI commands tailored to your needs.
- Open endless possibilities for integrating external APIs and advanced automation.

Through this practical demonstration, you'll gain a versatile technique for enhancing your development workflow in Cursor IDE.

[https://github.com/johnlindquist/mcp-cursor-tool-starter](https://github.com/johnlindquist/mcp-cursor-tool-starter)

Build MCP Tools Using Project Context for Custom Cursor IDE Automation

Setting up custom MCP (Machine Command Protocol) servers in Cursor can involve tedious steps, such as configuring node paths or referencing additional commands. This lesson shows how to streamline this process by bundling your MCP server directly into a standalone executable.

Workflow demonstrated in this lesson:

- Use a simple MCP server project starter.
- Run a single bundling command to create an executable.
- Right-click the generated executable, copy its full path, and add that directly to your Cursor settings.

Key benefits:

- Eliminates the need for complex node path configurations.
- Simplifies the setup and integration of custom MCP servers into Cursor.
- Makes the server executable instantly accessible within your Cursor environment.

By following this streamlined approach, you can quickly and easily integrate custom MCP servers into Cursor, making your development workflow cleaner and more efficient.

[https://github.com/johnlindquist/mcp-cursor-tool-starter]()

Easy MCP Server Setup in Cursor IDE with Bundled Executables

TanStack Router is the foundation for TanStack Start, which is gaining significant attention due to its innovative approach to application development.

This course focuses on getting effective TanStack Router, a modern and scalable routing solution for React applications. You will learn how to:
- set up and scaffold new applications,
- use file-based routing
- create nested routes
- manage dynamic route parameters and more.

The course covers advanced features like route loaders, caching strategies, and lifecycle hooks, which are crucial for enhancing application performance and user experience.

By understanding TanStack Router, you can build more efficient, type-safe, and maintainable applications, leveraging its integration with data fetching libraries like TanStack Query.

This knowledge is essential for developers looking to improve their routing skills and stay ahead in the field.

Tomasz Ducin

Up and Running with Tanstack Router and React

Learn TanStack Router for React: set up apps, use file-based routing, manage routes, and boost app performance.


In this lesson, we explore how TanStack Router integrates with the [native browser history API](https://developer.mozilla.org/en-US/docs/Web/API/History) to manage navigation.

As we navigate through different routes, the URL changes are stored in the browser's history, allowing users to use the forward and backward buttons to traverse their navigation history.

This functionality also **enables permalinks**, meaning users can copy and paste URLs to access specific routes directly.

Additionally, we learn how to programmatically interact with the history object to move forward or backward through the navigation stack, enhancing the user experience by providing full control over navigation actions.

This compatibility with the native history API ensures that TanStack Router applications behave similarly to traditional websites, offering a seamless and intuitive user experience.

Browse History in Tanstack Router

Browse history in TanStack React Router using the native history API for seamless navigation

In this lesson, we explore how to hook into TanStack Router's lifecycle hooks to execute custom logic during route changes.

The hooks we'll look into are: `onEnter`, `onStay`, and `onLeave`, which are triggered when entering, staying within, or leaving a route, respectively.

All hooks receive a detailed match parameter, providing information about the route's path, ID, and tons of other details.

This allows for the implementation of features like animations or logging when navigating between routes.

We also learn how to use these hooks to track and manage state changes as users interact with the application, making it easier to implement complex behaviors based on route transitions.

Hook into Route Lifecycle Hooks in Tanstack Router

Hook into TanStack React Router's lifecycle hooks for custom route logic and animations.

In this lesson, we learn how to handle not found errors in TanStack Router by using the `notFoundComponent` at both nested and global levels.

To trigger the display of a `notFoundComponent`, we must throw a specific error using the `notFound` function within a loader or other lifecycle method of a route. This approach allows us to provide custom error messages for specific routes or globally across the application.

We explore how to define a notFoundComponent within a specific route's configuration and how to set a `defaultNotFoundComponent` at the router global level, which applies to all routes unless overridden locally. This flexibility ensures that users receive meaningful feedback when encountering non-existent routes.

Provide NotFoundComponent at Nested Route or Global Level in Tanstack Router

Handle notFound errors in TanStack Router with notFoundComponent at nested or global levels.



In this lesson, we learn how to access dynamic route parameters using the `useParams` hook in TanStack Router.

When used with a specific `Route` object, `useParams` provides type-safe access to route parameters, ensuring that TypeScript knows the exact types of these parameters.

This approach eliminates the possibility of undefined/optional values, making it safer for accessing parameters like `employeeId`.

However, when using `useParams` globally without specifying a route, it requires an options object with `{ strict: false }`, which reduces type safety.

In this case, the hook can access parameters from any route in the application, but it does not guarantee their existence or type. This flexibility allows components to be reused across different routes, but it requires careful handling of potential errors.



Access Dynamic Route Parameters with useParams in Tanstack Router

Access dynamic route parameters with useParams in TanStack React Router for type-safe routing.

In this lesson, we learn how to reorganize file-based routes in TanStack Router to accommodate nested routing structures.

We explore how to create additional nested routes by converting files into directories, allowing for further nesting.

For example, to create a nested route like `/employees/$employeeId/edit`, we can create a **directory** (!) named `$employeeId` and place an `index.tsx` file inside it to define the route component for this nested route.

This approach provides flexibility in organizing files while maintaining the convention that file names and locations align with route paths. We also see how to adapt existing components and loaders to work with these reorganized routes, enabling features like edit forms or delete actions (or whatever) within nested routes.


Reorganize File-Based Routes in Tanstack Router

Reorganize file-based routes in TanStack Router for flexible nested routing.



In this lesson, we learn how to parametrize the loader for a nested route in TanStack Router.

We focus on a nested route like `/employees/$employeeId`, where the `$employeeId` is a **dynamic parameter**.

To fetch data for this route, we use a `loader` function that accesses the `$employeeId` parameter. This is achieved by using the params object available in the `loader` function, which contains the dynamic segments of the URL. We then use this parameter to call a function like `getEmployeeById`, which fetches specific employee details from an API.

We highlights that TanStack Router **automatically infers types** for these parameters, ensuring type safety for nested routes.

Parametrize Route Loader for Nested Route in Tanstack Router

Parametrize nested route loaders in TanStack Router using path parameters

Kyle Shevlin

Manage Complex Tic Tac Toe Game State in React

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