Implement a deep clone function that handles objects, arrays, dates, and circular references.

Recursive Clone with WeakMap for Cycles

Recursively traverse the object, using a WeakMap to track already-cloned objects and break circular references. Handle each type specifically.

function deepClone(obj, seen = new WeakMap()) {
  // Primitives and null
  if (obj === null || typeof obj !== 'object') return obj;

  // Circular reference check
  if (seen.has(obj)) return seen.get(obj);

  // Special types
  if (obj instanceof Date) return new Date(obj.getTime());
  if (obj instanceof RegExp) return new RegExp(obj.source, obj.flags);
  if (obj instanceof Map) {
    const map = new Map();
    seen.set(obj, map);
    obj.forEach((val, key) => map.set(deepClone(key, seen), deepClone(val, seen)));
    return map;
  }
  if (obj instanceof Set) {
    const set = new Set();
    seen.set(obj, set);
    obj.forEach(val => set.add(deepClone(val, seen)));
    return set;
  }

  // Arrays and plain objects
  const clone = Array.isArray(obj) ? [] : Object.create(Object.getPrototypeOf(obj));
  seen.set(obj, clone);

  for (const key of Reflect.ownKeys(obj)) {
    clone[key] = deepClone(obj[key], seen);
  }
  return clone;
}