calculate-square.js

function calculateSquare(matrix, chunkSize, randomFactor) {
  const half = chunkSize / 2;
  for (let y = 0; y < matrix.length; y += half) {
    for (let x = (y + half) % chunkSize; x < matrix.length; x += chunkSize) {
      const BOTTOM = matrix[y + half] ? matrix[y + half][x] : null;
      const LEFT = matrix[y][x - half];
      const TOP = matrix[y - half] ? matrix[y - half][x] : null;
      const RIGHT = matrix[y][x + half];
      const { count, sum } = [BOTTOM, LEFT, TOP, RIGHT].reduce(
        (result, value) => {
          if (isFinite(value) && value != null) {
            result.sum += value;
            result.count += 1;
          }
          return result;
        },
        { sum: 0, count: 0 }
      );
      matrix[y][x] = sum / count + randomInRange(-randomFactor, randomFactor);
    }
  }
  return matrix;
}