Search for a key in nested JavaScript objects

search_key.js

function searchKey(needle, haystack, depth) {
  var recur;
  recur = (obj, path, res, depth, key) => {
    if (key === needle) {
      res.push(path);
    }
    if (depth === 0) {
      return;
    }
    if ('object' === typeof obj && obj !== null) {
      var keys = Object.keys(obj);
      keys.forEach((k) => recur(obj[k], path+'.'+k, res, depth-1, k));
    }
  };
  var res = [];
  recur(haystack, '', res, depth, '');
  return res;
}

// Yields [".dontLook.myKey.monkey"]
searchKey('monkey', {dontLook: {myKey: {monkey: 3}, otherKey: false}}, 3);