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.

• Jaromanda X: when if (obj.id === id) is false, there is no return value

Answer 1

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);

Answer 2

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);