Find all values by specific key in a deep nested object

This is a bit late but for anyone else finding this, here is a clean, generic recursive function:

function findAllByKey(obj, keyToFind) {
  return Object.entries(obj)
    .reduce((acc, [key, value]) => (key === keyToFind)
      ? acc.concat(value)
      : (typeof value === 'object')
      ? acc.concat(findAllByKey(value, keyToFind))
      : acc
    , [])
}

// USAGE
findAllByKey(myObj, 'id')

I found steve's answer to be most suited for my needs in extrapolating this out and creating a general recursive function. That said, I encountered issues when dealing with nulls and undefined values, so I extended the condition to accommodate for this. This approach uses:

Array.reduce() - It uses an accumulator function which appends the value's onto the result array. It also splits each object into it's key:value pair which allows you to take the following steps:

1. Have you've found the key? If so, add it to the array;
2. If not, have I found an object with values? If so, the key is possibly within there. Keep digging by calling the function on this object and append the result onto the result array; and
3. Finally, if this is not an object, return the result array unchanged.

Hope it helps!

const myObj = {
  id: 1,
  children: [{
      id: 2,
      children: [{
        id: 3
      }]
    },
    {
      id: 4,
      children: [{
        id: 5,
        children: [{
          id: 6,
          children: [{
            id: 7,
          }]
        }]
      }]
    },
  ]
}

function findAllByKey(obj, keyToFind) {
  return Object.entries(obj)
    .reduce((acc, [key, value]) => (key === keyToFind)
      ? acc.concat(value)
      : (typeof value === 'object' && value)
      ? acc.concat(findAllByKey(value, keyToFind))
      : acc
    , []) || [];
}

const ids = findAllByKey(myObj, 'id');

console.log(ids)

You could make a recursive function like this:

idArray = []

function func(obj) {
  idArray.push(obj.id)
  if (!obj.children) {
    return
  }

  obj.children.forEach(child => func(child))
}

Snippet for your sample:

const myObj = {
  id: 1,
  children: [{
      id: 2,
      children: [{
        id: 3
      }]
    },
    {
      id: 4,
      children: [{
        id: 5,
        children: [{
          id: 6,
          children: [{
            id: 7,
          }]
        }]
      }]
    },
  ]
}

idArray = []

function func(obj) {
  idArray.push(obj.id)
  if (!obj.children) {
    return
  }

  obj.children.forEach(child => func(child))
}

func(myObj)
console.log(idArray)