Island Perimeter

let islandPerimeter = function(grid) {

    if (!grid || !grid.length) return 0;

    let maxRow = grid.length,
        maxCol = grid[0].length,
        LAND = 1, VISITED = 2;

    function calculatePerimeter(row, col) {

        if (grid[row][col] === LAND) {
            grid[row][col] = VISITED;

            let perimeter = 4;
            // check above;
            if (row > 0
                && (grid[row - 1][col] === LAND || grid[row - 1][col] === VISITED)) {
                perimeter = perimeter - 1;
                perimeter += calculatePerimeter(row - 1, col);
            }

            // check below;
            if (row < maxRow - 1
                && (grid[row + 1][col] === LAND || grid[row + 1][col] === VISITED)) {
                perimeter = perimeter - 1;
                perimeter += calculatePerimeter(row + 1, col);
            }

            // check left;
            if (col > 0
                && (grid[row][col - 1] === LAND || grid[row][col - 1] === VISITED)) {
                perimeter = perimeter - 1;
                perimeter += calculatePerimeter(row, col - 1);
            }

            // check right;
            if (col < maxCol - 1
                && (grid[row][col + 1] === LAND || grid[row][col + 1] === VISITED)) {
                perimeter = perimeter - 1;
                perimeter += calculatePerimeter(row, col + 1);
            }

            return perimeter; //?
        }

        return 0;
    }

    for (let row = 0; row < maxRow; row++) {
        for (let col = 0; col < maxCol;col++) {
            if (grid[row][col] === LAND) {
                return calculatePerimeter(row, col);
            }
        }
    }

    return 0;

};