```html
Snake
Snake
Score: 0
High: 0
Arrow keys or WASD to move · Space to start/pause · R to restart
```
```typescript
type Cell = { x: number; y: number };
type Direction = { x: number; y: number };
const GRID = 20;
const CELL = 20;
const INITIAL_TICK_MS = 150;
const MIN_TICK_MS = 60;
const SPEEDUP_EVERY = 5;
const SPEEDUP_DELTA = 10;
const COLOR_BG = "#000";
const COLOR_BODY = "#3aa635";
const COLOR_HEAD = "#7ed957";
const COLOR_FOOD = "#c0392b";
const COLOR_TEXT = "#fff";
const HIGH_KEY = "snake.high";
class Game {
private canvas: HTMLCanvasElement;
private ctx: CanvasRenderingContext2D;
private scoreEl: HTMLElement;
private highEl: HTMLElement;
private snake!: Cell[];
private dir!: Direction;
private pendingDir: Direction | null = null;
private food!: Cell;
private score!: number;
private high!: number;
private tickMs!: number;
private alive!: boolean;
private started!: boolean;
private paused!: boolean;
private timer: number | null = null;
constructor(canvas: HTMLCanvasElement, scoreEl: HTMLElement, highEl: HTMLElement) {
this.canvas = canvas;
const ctx = canvas.getContext("2d");
if (!ctx) throw new Error("no 2d context");
this.ctx = ctx;
this.scoreEl = scoreEl;
this.highEl = highEl;
// TODO: load high score from localStorage key HIG_KEY (parse Number, default 0) and call this.resetState() and this.render()
this.high = parseInt(localStorage.getItem(HIGH_KEY) || "0");
this.resetState();
this.render();
}
/** Begin the game on first Space press: started=true, paused=false, start the tick interval. No-op if already started. */
start(): void {
if (!this.started) {
this.started = true;
this.paused = false;
this.timer = INITIAL_TICK_MS;
this.startTimer();
}
}
/** Toggle pause on/off during a running game. If not yet started, behave like start(). When unpausing, re-arm the interval. When pausing, clear it. */
togglePause(): void {
if (!this.started) return;
if (this.paused) {
this.timer = null;
this.paused = false;
this.startTimer();
} else {
this.timer = null;
this.paused = true;
}
}
/** Full reset to the initial paused-before-start state, then render. Clears the tick interval if running. */
restart(): void {
this.stopTimer();
this.resetState();
this.render();
}
/** Apply pendingDir if it is not the opposite of the current dir, then move the snake one cell, detect wall/self collisions, handle food, and render. Called once per tick interval. */
private step(): void {
if (!this.alive) return;
let newDir = this.dir;
if (this.pendingDir) {
const dx = this.pendingDir.x - this.dir.x;
const dy = this.pendingDir.y - this.dir.y;
// Check if the pending direction is valid (not 180 degree turn)
if (dx !== 0 || dy !== 0) {
newDir = this.pendingDir;
}
this.pendingDir = null;
}
this.dir = newDir;
const head = this.snake[0];
const newHead: Cell = { x: head.x + this.dir.x, y: head.y + this.dir.y };
// 1. Check collisions
if (this.wouldCollide(newHead, false)) {
this.alive = false;
this.stopTimer();
this.render(); // Render game over state
return;
}
// 2. Check food
let ateFood = false;
if (newHead.x === this.food.x && newHead.y === this.food.y) {
this.score++;
this.updateScoreDom();
this.spawnFood();
ateFood = true;
}
// 3. Move snake
this.snake.unshift(newHead);
if (!ateFood) {
this.snake.pop();
}
// 4. Speed adjustment
if (ateFood) {
if (this.score % SPEEDUP_EVERY === 0) {
this.tickMs = Math.max(MIN_TICK_MS, this.tickMs - SPEEDUP_DELTA);
this.startTimer(); // Re-arm the interval with the new speed
}
}
this.render();
}
/** Set snake (length 3 at (10,10), (9,10), (8,10) moving right), reset dir/pendingDir/score/tickMs/alive/started/paused, spawn food. */
private resetState(): void {
this.snake = [
{ x: 10, y: 10 },
{ x: 9, y: 10 },
{ x: 8, y: 10 }
];
this.dir = { x: 1, y: 0 }; // Right
this.pendingDir = null;
this.score = 0;
this.tickMs = INITIAL_TICK_MS;
this.alive = true;
this.started = false;
this.paused = true;
this.timer = null;
this.spawnFood();
}
/** Pick a random Cell that is not currently occupied by the snake. If no empty cell, treat as win (alive=false, render). */
private spawnFood(): void {
let newFood: Cell;
do {
newFood = {
x: Math.floor(Math.random() * GRID),
y: Math.floor(Math.random() * GRID)
};
} while (this.snake.some(cell => cell.x === newFood.x && cell.y === newFood.y));
this.food = newFood;
}
/** Update the score and high DOM elements with "Score: N" / "High: N". */
private updateScoreDom(): void {
this.scoreEl.textContent = `Score: ${this.score}`;
this.highEl.textContent = `High: ${this.high}`;
}
/** Clear and redraw the board: black bg, food, snake body, snake head (distinct color). On not-yet-started, draw centered "Press Space to start". On paused (after first start), draw centered "Paused". On game-over, draw centered "Game Over — press R to restart". Text 20px sans-serif white, centered. */
private render(): void {
this.ctx.fillStyle = COLOR_BG;
this.ctx.fillRect(0, 0, this.canvas.width, this.canvas.height);
this.drawFood();
this.drawSnake();
if (!this.started) {
this.drawCenteredText("Press Space to start", this.canvas.width / 2, this.canvas.height / 2);
} else if (this.paused) {
this.drawCenteredText("Paused", this.canvas.width / 2, this.canvas.height / 2);
} else if (!this.alive) {
this.drawCenteredText("Game Over — press R to restart", this.canvas.width / 2, this.canvas.height / 2);
}
}
/** True iff `cell` lies inside the grid AND is not occupied by `snake` (excluding the soon-to-vacate tail when not growing). */
private wouldCollide(cell: Cell, willGrow: boolean): boolean {
// Check boundaries
if (cell.x < 0 || cell.x >= GRID || cell.y < 0 || cell.y >= GRID) {
return true; // Wall collision
}
// Check self collision (excluding the tail if growing)
for (const snakeCell of this.snake) {
if (snakeCell.x === cell.x && snakeCell.y === cell.y) {
// If growing, the tail position is about to be vacated, so we ignore collision with the tail.
if (willGrow && snakeCell === this.snake[this.snake.length - 1]) {
continue;
}
return true; // Self collision
}
}
return false;
}
private drawFood(): void {
this.ctx.fillStyle = COLOR_FOOD;
this.ctx.fillRect(this.food.x * CELL, this.food.y * CELL, CELL, CELL);
}
private drawSnake(): void {
this.snake.forEach((cell, index) => {
if (index === 0) {
// Head
this.ctx.fillStyle = COLOR_HEAD;
} else {
// Body
this.ctx.fillStyle = COLOR_BODY;
}
this.ctx.fillRect(cell.x * CELL, cell.y * CELL, CELL, CELL);
});
}
private drawCenteredText(text: string, x: number, y: number): void {
this.ctx.fillStyle = COLOR_TEXT;
this.ctx.font = "20px sans-serif";
this.ctx.textAlign = "center";
this.ctx.fillText(text, x, y);
}
private startTimer(): void {
if (this.timer === null) {
this.timer = this.tickMs;
this.timerId = setInterval(() => this.step(), this.tickMs);
}
}
private stopTimer(): void {
if (this.timer !== null) {
clearInterval(this.timerId);
this.timer = null;
}
}
}
// ---- top-level wiring (fill in) ----
const canvas = document.getElementById("game") as HTMLCanvasElement;
const scoreEl = document.getElementById("score") as HTMLElement;
const highEl = document.getElementById("high") as HTMLElement;
const game = new Game(canvas, scoreEl, highEl);
// Input handling
const handleKeyDown = (e: KeyboardEvent) => {
const key = e.key.toLowerCase();
switch (key) {
case 'arrowup':
case 'w':
game.pendingDir = { x: 0, y: -1 };
e.preventDefault();
break;
case 'arrowdown':
case 's':
game.pendingDir = { x: 0, y: 1 };
e.preventDefault();
break;
case 'arrowright':
case 'd':
game.pendingDir = { x: 1, y: 0 };
e.preventDefault();
break;
case 'arrowleft':
case 'a':
game.pendingDir = { x: -1, y: 0 };
e.preventDefault();
break;
case ' ': // Space to start/pause
game.togglePause();
e.preventDefault();
break;
case 'r': // R to restart
game.restart();
e.preventDefault();
break;
}
};
window.addEventListener('keydown', handleKeyDown);
```