Camel Case Keys
Problem statement
Implement a function camelCaseKeys that takes an object and returns a new object with all keys converted to camel case.
Camel case joins words together. The first word starts with a lowercase letter, and each following word starts with a capital letter.
Examples
camelCaseKeys({ "first_name": "Ada" });
// { firstName: "Ada" }
camelCaseKeys({
"user-id": 1,
"profile data": { "display_name": "Ada" }
});
// { userId: 1, profileData: { displayName: "Ada" } }Requirements
- Convert keys written in snake case, kebab case, space-separated case, or mixed separator case.
- Return a new object. Do not mutate the original input.
- Recursively convert keys inside nested plain objects.
- Recursively handle objects inside arrays.
- Keep primitive values,
Date,RegExp,Map,Set, functions, andnullunchanged.
Requirements & constraints
- Do not mutate the input object.
- Do not use external libraries.
- The function should support nested objects and arrays.
- Only plain object keys should be converted.
Examples
Example 1
Input: { "first_name": "Ada", "last-name": "Lovelace" }
Output: { firstName: "Ada", lastName: "Lovelace" }
Example 2
Input: { "profile data": { "avatar_url": "/ada.png" } }
Output: { profileData: { avatarUrl: "/ada.png" } }
How to approach Camel Case Keys
The strategy an interviewer expects you to reach for.
Camel-case keys rewrites object trees from API snake_case into JS-friendly keys without destroying arrays/primitives. Naive move Rename only the top level, or mutate the input object in place. Where it breaks Nested objects need recursion. Arrays should map elements, not become objects. Date/non-plain objects may need to pass through unchanged. The fix Split keys on non-alphanumeric separators, lowercase the first part, Capitalize the rest. Walk plain objects/arrays recursively into a new structure. Remember: New tree; recurse into plain objects/arrays; leave true primitives alone. Say this in the interview: I'd convert each key to camelCase, recurse through plain objects and arrays into a new structure, and avoid mutating the input.
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