[[0,1,0,0],
 [1,1,1,0],
 [0,1,0,0],
 [1,1,0,0]]

/**
 * @param {number[][]} grid
 * @return {number}
 */
var islandPerimeter = function(grid) {
  const getWaterNeighborAt = position => {
    if (!grid[position.y][position.x]) { return 0; }

    const north = position.y - 1 < 0 ? true : grid[position.y - 1][position.x] === 0;
    const east = position.x + 1 >= grid[0].length ? true : grid[position.y][position.x + 1] === 0;
    const south = position.y + 1 >= grid.length ? true : grid[position.y + 1][position.x] === 0;
    const west = position.x - 1 < 0 ? true : grid[position.y][position.x - 1] === 0;

    return north + east + south + west;
  };
  let perimeter = 0;
  grid.forEach((row, y) => {
    row.forEach((_, x) => {
      perimeter += getWaterNeighborAt({x, y});
    });
  });
  return perimeter;
};