### cleanObj

Removes any properties except the ones specified from a JSON object.

Use `Object.keys()` method to loop over given JSON object and deleting keys that are not included in given array.
If you pass a special key,`childIndicator`, it will search deeply apply the function to inner objects, too.

```js
const cleanObj = (obj, keysToKeep = [], childIndicator) => {
  Object.keys(obj).forEach(key => {
    if (key === childIndicator) {
      cleanObj(obj[key], keysToKeep, childIndicator);
    } else if (!keysToKeep.includes(key)) {
      delete obj[key];
    }
  });
  return obj;
};
```

```js
const testObj = { a: 1, b: 2, children: { a: 1, b: 2 } };
cleanObj(testObj, ['a'], 'children'); // { a: 1, children : { a: 1}}
```