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Build a Space Game Part 6: End and Restart

Every great game needs a satisfying conclusion and the ability to play again. In this final lesson of our space game series, you'll learn how to implement end conditions that determine when your game finishes and how to give players the option to restart for another adventure. These concepts are fundamental to creating engaging, replayable gaming experiences.

You've built an impressive space game with movement, collision detection, and scoring systems. Now you'll add the finishing touches that transform your project from a technical demo into a complete, polished game. Understanding end conditions and restart mechanics will also prepare you for building more complex games in the future.

By the end of this lesson, you'll have a fully functional space game with win/lose conditions, restart capabilities, and a smooth user experience. Let's bring your space game to its epic conclusion and make it infinitely replayable!

Pre-Lecture Quiz

Pre-lecture quiz

Understanding Game End Conditions

Game end conditions define when your game concludes and what triggers that conclusion. These conditions create goals for players and provide clear feedback about their performance. Let's explore the most common end condition patterns you can implement in your space game.

There are different ways to express an end condition in a game. It's up to you as the creator of the game to say why the game has ended. Here are some reasons, if we assume we are talking about the space game you have been building so far:

N Enemy ships have been destroyed: It's quite common if you divide up a game into different levels that you need to destroy N Enemy ships to complete a level
Your ship has been destroyed: There are definitely games where you lose the game if your ship is destroyed. Another common approach is that you have the concept of lives. Every time a your ship is destroyed it deducts a life. Once all lives have been lost then you lose the game.
You've collected N points: Another common end condition is for you to collect points. How you get points is up to you but it's quite common to assign points to various activities like destroying an enemy ship or maybe collect items that items drop when they are destroyed.
Complete a level: This might involve several conditions such as X enemy ships destroyed, Y points collected or maybe that a specific item has been collected.

Implementing Game Restart Functionality

Restart functionality is essential for creating an engaging gaming experience. When players enjoy your game, they'll want to play again immediately without having to reload the page or navigate away. A smooth restart mechanism keeps players engaged and provides opportunities to improve their performance.

Think about your favorite games - the best ones make it effortless to jump into another round. We'll implement a restart system that clears the previous game state and initializes everything fresh for a new adventure.

✅ Reflection: Think about the games you've played. Under what conditions do they end, and how are you prompted to restart? What makes a restart experience feel smooth versus frustrating?

What You'll Build

In this lesson, you'll implement the final features that complete your space game experience. These additions will transform your game from a technical demonstration into a polished, replayable experience.

Game completion features you'll add:

Victory condition: Once all enemy ships are destroyed, the game ends with a celebration message
Defeat condition: When the player's lives reach zero, the game ends with a defeat message
Restart mechanism: Players can press Enter to start a fresh game after winning or losing
State management: The game properly clears previous state and reinitializes all systems

Getting Started

Before implementing the end conditions, let's set up your development environment and review the project structure. You'll be working with the files from your previous space game lessons.

Your project structure should contain:

-| assets
  -| enemyShip.png
  -| player.png
  -| laserRed.png
  -| life.png
-| index.html
-| app.js
-| package.json

To start your development server:

cd your-work
npm start

Here's what this command does:

Starts a local HTTP server on http://localhost:5000
Serves your game files with proper MIME types
Enables live development with automatic reloading

Open your browser and navigate to http://localhost:5000. Your game should be in a playable state from the previous lessons.

💡 Pro Tip: To avoid warnings in Visual Studio Code, declare gameLoopId at the top of your file as let gameLoopId; instead of declaring it inside the window.onload function. This follows modern JavaScript variable declaration best practices.

Implementation Steps

Step 1: Create End Condition Tracking Functions

First, you'll create utility functions that check the current state of your game. These functions will help determine when the game should end based on different victory or defeat conditions.

function isHeroDead() {
  return hero.life <= 0;
}

function isEnemiesDead() {
  const enemies = gameObjects.filter((go) => go.type === "Enemy" && !go.dead);
  return enemies.length === 0;
}

Breaking down what happens here:

Checks if the hero's life has reached zero or below
Filters the game objects to find only living enemy ships
Returns true when all enemies have been destroyed
Uses the logical comparison operators to create clear boolean results
Leverages array filtering to efficiently count remaining enemies

Step 2: Update Event Handlers for End Conditions

Next, you'll modify your existing event handlers to check for end conditions after each collision. This ensures your game responds immediately when victory or defeat conditions are met.

eventEmitter.on(Messages.COLLISION_ENEMY_LASER, (_, { first, second }) => {
    first.dead = true;
    second.dead = true;
    hero.incrementPoints();

    if (isEnemiesDead()) {
      eventEmitter.emit(Messages.GAME_END_WIN);
    }
});

eventEmitter.on(Messages.COLLISION_ENEMY_HERO, (_, { enemy }) => {
    enemy.dead = true;
    hero.decrementLife();
    if (isHeroDead())  {
      eventEmitter.emit(Messages.GAME_END_LOSS);
      return; // loss before victory
    }
    if (isEnemiesDead()) {
      eventEmitter.emit(Messages.GAME_END_WIN);
    }
});

eventEmitter.on(Messages.GAME_END_WIN, () => {
    endGame(true);
});
  
eventEmitter.on(Messages.GAME_END_LOSS, () => {
  endGame(false);
});

Here's what this code accomplishes:

Handles laser-enemy collisions by marking both objects as dead
Increments the player's score when enemies are destroyed
Checks for victory condition after each enemy destruction
Manages hero-enemy collisions by reducing player lives
Prioritizes defeat over victory to prevent conflicting end states
Triggers appropriate end game sequences based on conditions met

Step 3: Add New Message Constants

You'll need to add new message types to your Messages constant object. These constants help maintain consistency and prevent typos in your event system.

GAME_END_LOSS: "GAME_END_LOSS",
GAME_END_WIN: "GAME_END_WIN",

In the above, we've:

Added constants for game end events to maintain consistency
Used descriptive names that clearly indicate the event purpose
Followed the existing naming convention for message types

Step 4: Implement Restart Controls

Now you'll add keyboard controls that allow players to restart the game. The Enter key is a natural choice since it's commonly associated with confirming actions and starting new games.

Add Enter key detection to your existing keydown event listener:

else if(evt.key === "Enter") {
   eventEmitter.emit(Messages.KEY_EVENT_ENTER);
}

Add the new message constant:

KEY_EVENT_ENTER: "KEY_EVENT_ENTER",

What you need to know:

Extends your existing keyboard event handling system
Uses the Enter key as the restart trigger for intuitive user experience
Emits a custom event that other parts of your game can listen for
Maintains the same pattern as your other keyboard controls

Step 5: Create the Message Display System

Your game needs a way to communicate victory, defeat, and restart instructions to players. You'll create a flexible message display function that can show different types of messages with appropriate styling.

Create the displayMessage() function:

function displayMessage(message, color = "red") {
  ctx.font = "30px Arial";
  ctx.fillStyle = color;
  ctx.textAlign = "center";
  ctx.fillText(message, canvas.width / 2, canvas.height / 2);
}

Step by step, here's what's happening:

Sets the font size and family for clear, readable text
Applies a color parameter with "red" as the default for warnings
Centers the text horizontally and vertically on the canvas
Uses modern JavaScript default parameters for flexible color options
Leverages the canvas 2D context for direct text rendering

Create the endGame() function:

function endGame(win) {
  clearInterval(gameLoopId);

  // Set a delay to ensure any pending renders complete
  setTimeout(() => {
    ctx.clearRect(0, 0, canvas.width, canvas.height);
    ctx.fillStyle = "black";
    ctx.fillRect(0, 0, canvas.width, canvas.height);
    if (win) {
      displayMessage(
        "Victory!!! Pew Pew... - Press [Enter] to start a new game Captain Pew Pew",
        "green"
      );
    } else {
      displayMessage(
        "You died !!! Press [Enter] to start a new game Captain Pew Pew"
      );
    }
  }, 200)  
}

Understanding this function:

Stops the game loop immediately to prevent further updates
Waits 200 milliseconds to ensure all pending canvas operations complete
Clears the entire canvas and fills it with a black background
Displays conditional messages based on victory or defeat
Uses green text for victory and red text (default) for defeat
Provides clear instructions for restarting the game

Step 6: Implement Game Reset Functionality

The reset system needs to completely clean up the current game state and initialize a fresh game session. This ensures players get a clean start without any leftover data from the previous game.

Create the resetGame() function:

function resetGame() {
  if (gameLoopId) {
    clearInterval(gameLoopId);
    eventEmitter.clear();
    initGame();
    gameLoopId = setInterval(() => {
      ctx.clearRect(0, 0, canvas.width, canvas.height);
      ctx.fillStyle = "black";
      ctx.fillRect(0, 0, canvas.width, canvas.height);
      drawPoints();
      drawLife();
      updateGameObjects();
      drawGameObjects(ctx);
    }, 100);
  }
}

Let's understand each part:

Checks if a game loop is currently running before resetting
Clears the existing game loop to stop all current game activity
Removes all event listeners to prevent memory leaks
Reinitializes the game state with fresh objects and variables
Starts a new game loop with all the essential game functions
Maintains the same 100ms interval for consistent game performance

Add the Enter key event handler to your initGame() function:

eventEmitter.on(Messages.KEY_EVENT_ENTER, () => {
  resetGame();
});

Add the clear() method to your EventEmitter class:

clear() {
  this.listeners = {};
}

Key points to remember:

Connects the Enter key press to the reset game functionality
Registers this event listener during game initialization
Provides a clean way to remove all event listeners when resetting
Prevents memory leaks by clearing event handlers between games
Resets the listeners object to an empty state for fresh initialization

Congratulations! 🎉

👽 💥 🚀 Fantastic work, Captain! Your space game is now complete with proper end conditions and restart functionality! You've successfully built a fully functional game that players can enjoy again and again. 🚀 💥 👽

What you've accomplished:

Implemented victory and defeat conditions that respond to game events
Created a smooth restart system that clears previous game state
Built an intuitive user interface for game completion messages
Designed a replayable gaming experience with proper state management
Applied modern JavaScript patterns for event handling and game flow

GitHub Copilot Agent Challenge 🚀

Use the Agent mode to complete the following challenge:

Description: Enhance the space game by implementing a level progression system with increasing difficulty and bonus features.

Prompt: Create a multi-level space game system where each level has more enemy ships with increased speed and health. Add a scoring multiplier that increases with each level, and implement power-ups (like rapid fire or shield) that randomly appear when enemies are destroyed. Include a level completion bonus and display the current level on screen alongside the existing score and lives.

🚀 Optional Enhancement Challenge

Add Audio to Your Game: Enhance your gameplay experience by implementing sound effects! Consider adding audio for:

Laser shots when the player fires
Enemy destruction when ships are hit
Hero damage when the player takes hits
Victory music when the game is won
Defeat sound when the game is lost

Audio implementation example:

// Create audio objects
const laserSound = new Audio('assets/laser.wav');
const explosionSound = new Audio('assets/explosion.wav');

// Play sounds during game events
function playLaserSound() {
  laserSound.currentTime = 0; // Reset to beginning
  laserSound.play();
}