matrix_sketch.js

// Matrix with a strided array

class Matrix {
  constructor (rows, cols) {
    this.rows = rows;
    this.cols = cols;
    this.data = Array(rows * cols).fill(null);
  }
  
  get(x, y) {
    return this.data[x + y * this.cols];
  }
  
  set(x, y, val) {
    this.data[x + y * this.cols] = val;
  }
  
  neighbors(row, col) {
    // translate offsets and return neighbor cells
    return [
      [0, -1],
      [0, 1],
      [1, 1],
      [1, -1],
      [-1, 1],
      [-1, -1],
      [1, 0],
      [-1, 0]
    ].map(coords => {
      return this.get(row + coords[0], col + coords[1]);
    })
  }
}

let grid = new Matrix(4, 5);

grid.set(0, 0, "asteroid");
grid.set(1, 2, "ship");
grid.set(0, 2, "asteroid");

console.log(grid.get(1, 1), grid.data);
console.log(grid.neighbors(1, 3));