function concatAndSort(arr) {
  console.log(arr.toString().split(',').map(x => Number(x)).sort((a, b) => a - b));
}

concatAndSort([[1,2,3],
        [8,9,4],
        [7,6,5],
        [12,456,54,3],
        [23,6,864],
        [43,453],
        [7,234,6]
      ]); // [ 1, 2, 3, 3, 4, 5, 6, 6, 6, 7, 7, 8, 9, 12, 23, 43, 54, 234, 453, 456, 864 ]