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

TASK: Deep Clone an Object

Write a function 'deepClone(obj)' that deeply copies a given JavaScript object or array (including nested objects, arrays and primitives) without sharing references. It must also clone Date and RegExp objects.

STARTER CODE (javascript):
function deepClone(obj) {
  // Write your code here
}

module.exports = { deepClone };


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 deepClone(obj) {
  const seen = new WeakMap();

  function clone(value) {
    // Primitives and functions (treated as references)
    if (value === null || typeof value !== 'object') return value;

    // Handle circular references
    if (seen.has(value)) return seen.get(value);

    // Date
    if (value instanceof Date) {
      const copy = new Date(value.getTime());
      seen.set(value, copy);
      return copy;
    }

    // RegExp
    if (value instanceof RegExp) {
      const copy = new RegExp(value.source, value.flags);
      seen.set(value, copy);
      return copy;
    }

    // Array
    if (Array.isArray(value)) {
      const copy = [];
      seen.set(value, copy);
      value.forEach((item, idx) => {
        copy[idx] = clone(item);
      });
      return copy;
    }

    // Plain Object (or other objects)
    const copy = Object.create(Object.getPrototypeOf(value));
    seen.set(value, copy);
    const keys = Reflect.ownKeys(value);
    for (const key of keys) {
      const desc = Object.getOwnPropertyDescriptor(value, key);
      if (desc) {
        if (desc.hasOwnProperty('value')) {
          desc.value = clone(desc.value);
        }
        Object.defineProperty(copy, key, desc);
      } else {
        // Fallback
        copy[key] = clone(value[key]);
      }
    }
    return copy;
  }

  return clone(obj);
}

module.exports = { deepClone };
```