recursive function for nested object returning undefined

Question

I'm looping through a nested object of objects, looking for a specific object and if I'm I find it, I do stuff. I can get it working for the first nest, but any nest after that I get an undefined value.

let myObj = [{
    id: 1,
    children: [{
        id: 1.1,
        children: []
      },
      {
        id: 1.2,
        children: []
      }
    ]
  },
  {
    id: 2,
    children: [{
        id: 2.1,
        children: []
      },
      {
        id: 2.2,
        children: []
      }
    ]
  }
]


function addToObj(itemToAdd, parentId, obj) {

  for (let i = 0; i < obj.length; i++) {

    const item = search(obj[i], parentId);

    console.log(item); // undefined

    if (item) {
      item.children = item.children.concat(itemToAdd);
      break;
    }
  }

  function search(obj, id) {
    if (obj.id === id) {
      console.log(obj); // defined (obj with id of 2.1), but returns undefined?
      return obj;
    }

    for (let i = 0; i < obj.children.length; i++) {
      search(obj.children[i], id);
    }
  }

  return obj;
};

const itemToAdd = {
  id: 100,
}

addToObj(itemToAdd, 2.1, myObj);

The function in the above snippet loops through the object, looking for a specific item. If it finds the item it will insert an object into that items children property.

when if (obj.id === id) is false, there is no return value — Jaromanda X
– Jaromanda X, Commented Mar 17, 2019 at 7:32

CertainPerformance · Accepted Answer · 2019-03-17 07:32:42Z

You need to use the return value from the recursive search: if it exists, return it:

for (let i = 0; i < obj.children.length; i++) {
  const possibleResult = search(obj.children[i], id);
  if (possibleResult) {
    return possibleResult;
  }
}

let myObj = [{
    id: 1,
    children: [{
        id: 1.1,
        children: []
      },
      {
        id: 1.2,
        children: []
      }
    ]
  },
  {
    id: 2,
    children: [{
        id: 2.1,
        children: []
      },
      {
        id: 2.2,
        children: []
      }
    ]
  }
]


function addToObj(itemsToAdd, parentId, obj) {

  for (let i = 0; i < obj.length; i++) {

    const item = search(obj[i], parentId);

    // first log here will be undefined, nothing found
    // second log here will find the object
    console.log('item', item);

    if (item) {
      item.children = item.children.concat(itemsToAdd);
      break;
    }
  }

  function search(obj, id) {
    if (obj.id === id) {
      console.log('obj', obj); // defined (obj with id of 2.1), but returns undefined?
      return obj;
    }

    for (let i = 0; i < obj.children.length; i++) {
      const possibleResult = search(obj.children[i], id);
      if (possibleResult) {
        return possibleResult;
      }
    }
  }

  return obj;
};

const itemToAdd = {
  id: 100,
}

addToObj(itemToAdd, 2.1, myObj);

Maheer Ali · Accepted Answer · 2019-03-17 07:43:25Z

There are two problems in code

if (obj.id === id) is false then in loop you are returning nothing.
You should check if obj.children exists before loop.

let myObj = [
  {
    id: 1,
    children: [
    	{
      	id: 1.1,
        children: []
      },
      {
      	id: 1.2,
        children: []
      }
    ]
  },
  {
    id: 2,
    children: [
      {
        id: 2.1,
        children: []
      },
      {
      	id: 2.2,
        children: []
      }
    ]
  }
]

There are two problems in code:

 - List item

function addToObj(itemToAdd, parentId, obj) {

  for (let i=0;i<obj.length;i++) {

    const item = search(obj[i], parentId);

    console.log(item); // undefined

    if (item) {
      item.children = item.children.concat(itemToAdd);
      break;
    }
  }

  function search(obj, id) {
    if (obj.id === id) {
      console.log(obj); // defined (obj with id of 2.1), but returns undefined?
      return obj;
    }
    if(obj.children){
    
    for (let i=0;i<obj.children.length;i++) {
       let x = search(obj.children[i], id);
       if(x) return x;
      }
    }
  }

  return obj;
};

const itemToAdd = {
	id: 100,
}

addToObj(itemToAdd, 2.1, myObj);

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