Javascript function to iterate and modify all the nodes in a tree like javascript object

map-over-tree.js

let obj = {
  id: '1',
  children: [
    {
      id: '2',
      children: [
        {
          id: '4',
          children: [
            {
               id: '5',
               children: [
                  {
                    id: '6',                  
                  },
                  {
                    id: '7',                  
                  }
               ]
            }
          ]
        }
      ]
    },
    {
      id: '3',
    }
  ]
};

function mapTree(obj, mapFunction) {
  mapFunction(obj);
  if(obj.children) {
    obj.children.forEach((child, index) => {
        mapOverArray(child, mapFunction);
    });
  }
}

function modifyObject(obj) {
  obj.hello = obj.id + '_extended';
  obj.newProp = 'yeaah';
};

mapTree(obj, modifyObject);

console.log(JSON.stringify(obj, null, 2));