嵌套对象返回未定义的递归函数

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.

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);