Method constructor

ch5-game-of-life/gol.js:2–9

(size, buffer, paint = () => {})

class Grid {
  constructor(size, buffer, paint = () => {}) {
    const sizeSquared = size * size;
    this.buffer = buffer;
    this.size = size;
    this.cells = new Uint8Array(this.buffer, 0, sizeSquared);
    this.nextCells = new Uint8Array(this.buffer, sizeSquared, sizeSquared);
    this.paint = paint;
  }

  getCell(x, y) {
    const size = this.size;