flatKeys.js

const flatKeys = (object, keys = [], k = '') => {
  for (const key in object) {
    const rest = k.length ? '.' + key : key

    if (typeof object[key] === 'object' && !Array.isArray(object[key])) {
      flatKeys(object[key], keys, k + rest)
    } else {
      keys.push(k + rest)
    }
  }

  return keys
}