Flatten a 2D Array into a spiral format

spiral_matrix.js

//ES6
function spiral(matrix) {
    const arr = [];

    while (matrix.length) {
        arr.push(
            ...matrix.shift(),
            ...matrix.map(a => a.pop()),
            ...(matrix.pop() || []).reverse(),
            ...matrix.map(a => a.shift()).reverse()
        );
    }
    return arr;
}

const array2d = [[1,2,3],[4,5,6],[7,8,9],[10,11,12]];
const spiral_array = spiral(array2d);
spiral_array();
// Output: [1, 2, 3, 6, 9, 12, 11, 10, 7, 4, 5, 8]