How to get length of multidimensionnel array [duplicate]

Question

I want to get length of multidimentionnal array in JS : This is my array :

const treeData = [
  {
    title: '0-0',
    key: '0-0',
    children: [
      {
        title: '0-0-0',
        key: '0-0-0',
        children: [
          {
            title: '0-0-0-0',
            key: '0-0-0-0',
          },
          {
            title: '0-0-0-1',
            key: '0-0-0-1',
          },
          {
            title: '0-0-0-2',
            key: '0-0-0-2',
          },
        ],
      },
      {
        title: '0-0-1',
        key: '0-0-1',
        children: [
          {
            title: '0-0-1-0',
            key: '0-0-1-0',
          },
          {
            title: '0-0-1-1',
            key: '0-0-1-1',
          },
          {
            title: '0-0-1-2',
            key: '0-0-1-2',
          },
        ],
      },
      {
        title: '0-0-2',
        key: '0-0-2',
      },
    ],
  },
  {
    title: '0-1',
    key: '0-1',
    children: [
      {
        title: '0-1-0-0',
        key: '0-1-0-0',
      },
      {
        title: '0-1-0-1',
        key: '0-1-0-1',
      },
      {
        title: '0-1-0-2',
        key: '0-1-0-2',
      },
    ],
  },
  {
    title: '0-2',
    key: '0-2',
  },
];

The output should be : 15 The idea is to map trough all elements and if they have an array child, get the lentgh of it I'm sure that I will go for a récursive function but it seems to be tricky.. I did'nt found any solutions in internet, have you an idea please ? Thank you