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

TASK: Group Array Elements (groupBy)

Write a function 'groupBy(array, fnOrKey)' that takes an array of objects and either a property name or a selector function, and returns an object grouping the elements by that value.

STARTER CODE (javascript):
function groupBy(array, fnOrKey) {
  // Write your code here
}

module.exports = { groupBy };


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 groupBy(array, fnOrKey) {
  const result = {};

  for (let i = 0; i < array.length; i++) {
    const item = array[i];
    const key = typeof fnOrKey === "function" ? fnOrKey(item, i, array) : item[fnOrKey];

    if (!Object.prototype.hasOwnProperty.call(result, key)) {
      Object.defineProperty(result, key, {
        value: [],
        writable: true,
        enumerable: true,
        configurable: true
      });
    }

    result[key].push(item);
  }

  return result;
}

module.exports = { groupBy };
```