traverse matrix in spiral

spiral.ts

const a = [
    [1, 2, 3, 4, 5, 6],
    [1, 2, 3, 4, 5, 6],
    [1, 2, 3, 4, 5, 6],
    [1, 2, 3, 4, 5, 6],
    [1, 2, 3, 4, 5, 6],
    [1, 2, 3, 4, 5, 6],
];
enum Dir {
    east, south, west, north
}
const spiral = (matrix: number[][]): number[] => {
    let res = [];
    let [height, width] = [a.length, a[0].length];
    let [nw, ew, sw, ww] = [0, width-1, height-1, 0];
    let dir: Dir = Dir.east;
    let [x, y] = [-1, 0];
    while (res.length < width * height) {
        switch (dir) {
            case Dir.east:
                if (x < ew) {
                    x += 1;
                } else {
                    nw += 1;
                    dir = Dir.south;
                    continue;
                }
                break;
            case Dir.south:
                if (y < sw) {
                    y += 1;
                } else {
                    ew -= 1;
                    dir = Dir.west;
                    continue;
                }
                break;
            case Dir.west:
                if (x > ww) {
                    x -= 1;
                } else {
                    sw -= 1;
                    dir = Dir.north;
                    continue;
                }
                break;
            case Dir.north:
                if (y > nw) {
                    y -= 1;
                } else {
                    ww += 1;
                    dir = Dir.east;
                    continue;
                }
                break;
        }
        res.push(matrix[y][x]);
    }
    return res;
};

console.log(spiral(a));