[рони]

javascript888,

<script>
        let arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
        function normalizeArr(arr, cols, box) {
            let length = cols - (arr.length % cols || cols);
            for (; length--; ) arr.push(box);
            length = arr.length / cols;
            return Array.from({length}, (_, i) => arr.slice(i *= cols, i + cols));
        }
        document.write(JSON.stringify(normalizeArr(arr, 4, '-')));
    </script>