JavaScript utility implementation

Utility implementation tasks test closure state, timers, callbacks, and API contracts. Debounce delays until calls stop; throttle limits call frequency; memoize caches by key; EventEmitter stores listeners; Promise helpers coordinate asynchronous completion and errors.

Trade-off: compare time, memory, and implementation complexity before committing to a structure or pattern.

On interviews: Interviewers watch edge cases: preserving this and arguments, cleanup methods, leading or trailing calls, listener removal during emit, and rejection handling.

Common pitfalls: A happy-path implementation is rarely enough. Define timing semantics before code, avoid leaking timers or listeners, and make cache keys explicit for memoize.

Checklist:

• Define API contract.
• Preserve this and args.
• Clean timers and listeners.
• Test errors and edge timing.