Convert Between snake_case and camelCase Object Keys (Including Nested Objects)

Problem, as an interviewer would state it: "Write snakeToCamel(obj) and camelToSnake(obj) — recursively convert every object key between snake_case and camelCase, correctly handling nested objects and arrays of objects."

Examples:

snakeToCamel({ user_id: 1, address_info: { zip_code: "10001" } });
// { userId: 1, addressInfo: { zipCode: "10001" } }

Clarifying questions expected:

• Should this recurse into arrays too, converting keys of objects INSIDE an array value?
• What about keys that are already in the target case, or contain numbers?
• Should Date objects or other non-plain-object values be recursed into, or left alone?

Code / implementation expected: Yes — real, direct proof on a genuinely nested structure (object + array of objects), including a full round-trip back to the original.