===== ISTEM =====
Solve the following programming task.

TASK: Object Diff

Write a function 'objectDiff(obj1, obj2)' that compares two JavaScript objects and returns only the changed properties as [oldValue, newValue].

STARTER CODE (javascript):
function objectDiff(obj1, obj2) {
  // Write your code here
}

module.exports = { objectDiff };


RULES:
- Keep the function name and signature EXACTLY as given.
- Return working code only. No explanations.
- Put the code in a single ``` block.
- Try to solve it first. If you genuinely cannot, write only this single
  line instead of producing faulty code: CANNOT_SOLVE

===== HAM YANIT =====
```javascript
function objectDiff(obj1, obj2) {
  const result = {};
  const keys = new Set([...Object.keys(obj1 || {}), ...Object.keys(obj2 || {})]);

  for (const key of keys) {
    if (obj1?.[key] !== obj2?.[key]) {
      result[key] = [obj1?.[key], obj2?.[key]];
    }
  }

  return result;
}

module.exports = { objectDiff };
```