463. Island Perimeter

/** * @param {number[][]} grid * @return {number} */var islandPerimeter = function(grid) {    const rows = grid.length    const cols = grid[0].length    let perimeter  = 0    const isWater = (r, c) => {        return r < 0 || r >= rows || c < 0 || c >= cols || grid[r][c] === 0    }    for (let r = 0; r < rows; r++) {        for (let c = 0; c < cols; c++) {            if (grid[r][c] === 1) {                if (isWater(r - 1, c)) perimeter++                if (isWater(r + 1, c)) perimeter++                if (isWater(r, c - 1)) perimeter++                if (isWater(r, c + 1)) perimeter++            }        }    }    return perimeter};