Event Emitter (Mini Implementation)

What you’ll build / What this tests

This premium javascript coding focuses on Event Emitter (Mini Implementation). You’ll apply async and design-patterns thinking with intermediate level constraints. The prompt emphasizes Build a tiny event emitter with on, off, and emit. Store listeners per event, allow multiple….

Learning goals

• Translate the prompt into a clear javascript API signature and return shape.
• Apply async, design-patterns, oop techniques to implement event emitter (mini implementation).
• Handle intermediate edge cases without sacrificing readability.
• Reason about time/space complexity and trade-offs in javascript.

Key decisions to discuss

• Define the exact input/output contract before coding.
• Choose iteration vs higher-order methods for readability.
• Decide on concurrency and error propagation behavior.
• Prioritize predictable edge-case handling over micro-optimizations.

Evaluation rubric

• Correctness: covers required behaviors and edge cases.
• Clarity: readable structure and predictable control flow.
• Complexity: avoids unnecessary work for large inputs.
• API discipline: no mutation of inputs; returns expected shape.
• Testability: solution is easy to unit test.

Constraints / Requirements

• Preserve input order and handle empty arrays safely.
• Handle async flow without blocking the event loop.
• Return a Promise and resolve asynchronously without blocking.
• Handle empty or missing inputs without throwing errors.
• Keep runtime close to linear time where possible.
• Prefer a pure function: no side effects beyond the return value.

Mini snippet (usage only)

// Example usage
const input = /* event emitter (mini implementation) input */;
const result = solve(input);
console.log(result);

// Edge case check
const empty = input ?? null;
const fallback = solve(input);
console.log(fallback);

// Expected: describe output shape, not the implementation
// (no solution code in preview)

Common pitfalls

• Mutating inputs instead of returning a new value.
• Skipping edge cases like empty input, duplicates, or nulls.
• Forgetting to await or return the Promise.
• Overlooking time complexity for large inputs.

Related questions

• Create a Deferred Promise (For Async Tests)Free
• Promise.any (First Fulfilled)Free
• Run With a Performance Budget (Sync or Async)Free
• Sleep / Delay PromiseFree
• Fetch JSON with Timeout + AbortFree
• Poll Until (with Timeout + Abort)Free