Conway's Life

let grid, w, h, cell = 6;
function init({ width, height }) {
  w = Math.floor(width / cell);
  h = Math.floor(height / cell);
  grid = new Uint8Array(w * h);
  for (let i = 0; i < grid.length; i++) grid[i] = Math.random() < 0.25 ? 1 : 0;
}
function step() {
  const next = new Uint8Array(grid.length);
  for (let y = 0; y < h; y++) {
    for (let x = 0; x < w; x++) {
      let n = 0;
      for (let dy = -1; dy <= 1; dy++) {
        for (let dx = -1; dx <= 1; dx++) {
          if (dx === 0 && dy === 0) continue;
          const nx = (x + dx + w) % w;
          const ny = (y + dy + h) % h;
          n += grid[ny * w + nx];
        }
      }
      const i = y * w + x;
      next[i] = (grid[i] && (n === 2 || n === 3)) || (!grid[i] && n === 3) ? 1 : 0;
    }
  }
  grid = next;
}
let acc = 0;
function tick({ ctx, dt, width, height }) {
  acc += dt;
  if (acc > 0.06) { step(); acc = 0; }
  ctx.fillStyle = "#0a0a0a";
  ctx.fillRect(0, 0, width, height);
  ctx.fillStyle = "#34d399";
  for (let y = 0; y < h; y++) {
    for (let x = 0; x < w; x++) {
      if (grid[y * w + x]) ctx.fillRect(x * cell, y * cell, cell - 1, cell - 1);
    }
  }
}