Machine Coding & Refactoring Arena
Step-by-step engineering challenges graded from 1 to 10 Points. Write production code in our interactive editor, and receive instant, deep AI code reviews highlighting code smells, memory leaks, refactoring strategies, and staff-level solutions.
Robust Event Emitter with Wildcards & Scope Cleanup
Build a production-grade Pub/Sub Event Emitter supporting wildcard namespaces, listener priority, and auto-cleanup unsubscriptions.
Enterprise Deep Clone Engine with Circular Reference & Type Preservation
Implement a complete recursive deep clone engine handling circular object graphs, TypedArrays, Sets, Maps, and Symbol keys.
Async Promise Pool with Concurrency Limiter & Jittered Retries
Build an async worker queue that executes hundreds of async tasks with strict concurrency throttling, retry backoff with jitter, and AbortController.
Reactive Signal, Computed & Effect Engine from Scratch
Build a fine-grained reactive primitives system (Signals, Computed Signals, and Auto-Tracking Effects) with dependency graph cleanup and microtask batching.
High-Performance Virtualized List & Dynamic Windowing Engine
Implement a DOM-agnostic virtual list windowing algorithm computing visible indices, dynamic height caches, and overscan buffer offsets for 100,000+ items at 60 FPS.
Sliding-Window Log & Token Bucket Dual Rate Limiter
Build an API Rate Limiter implementing Token Bucket (for smooth bursts) and Sliding-Window Counter (for strict interval protection) with memory pruning.
Resilient WebSocket Client with Heartbeat, Auto-Reconnect & Offline Queue
Build an enterprise WebSocket connection manager featuring ping/pong heartbeat dead-socket detection, exponential jittered reconnection, and offline message queue replay.
Offline-First Optimistic Mutation Queue with Rollback & State Reconciliation
Build an optimistic UI mutation orchestrator managing local cache patching, rollback snapshots on server error, and offline sync replay with conflict resolution.
In-Memory MVCC Transactional Key-Value Store with Snapshot Isolation
Build an ACID in-memory key-value store with Multi-Version Concurrency Control (MVCC), transaction commit/rollback, and snapshot isolation.
Distributed Priority Job Scheduler with Lock Leasing & Dead-Letter Queue
Build a distributed priority task scheduler featuring min-heap priority queues, worker heartbeat lock leases, exponential backoff, and poison pill DLQ routing.
MEAN Stack: Angular & RxJS Debounced Autocomplete Search Engine
Build an Angular & RxJS search manager with debouncing, distinct query caching, TTL eviction, and request cancellation.
MEAN Stack: Express.js Composable Middleware Chain & RFC 7807 Error Boundary
Build an Express middleware pipeline runner supporting async NextFunction, JWT bearer parsing, NoSQL sanitization, and RFC 7807 error responses.
MEAN Stack: Angular Reactive Form Delta Tracker & Auto-Save Sync Engine
Design an Angular reactive form delta engine that computes dirty field patches, debounces auto-save triggers, and provides rollback recovery.
MERN Stack: React useAsync & useDebounce Hook with AbortController Cancellation
Implement a production-grade React async state manager with AbortController signal cleanup and stale response prevention.
MERN Stack: Lightweight Reactive State Store with Selectors & Middleware
Build a mini-Zustand/Redux state store with immutable patchState, selector memoization, and logger/persistence middleware.
MERN Stack: Axios/Fetch Interceptor with Silent JWT Token Refresh Queue
Implement an HTTP interceptor that catches 401s, pauses concurrent requests in a FIFO promise queue, refreshes the token, and replays failed requests.
MongoDB: In-Memory Query Matcher & Aggregation Pipeline Filter
Build an in-memory document query engine supporting $eq, $gt, $in, $regex, $and, $or, and $project/$sort pipeline stages.
MongoDB: Mongoose Schema Validator & Sanitizer Engine
Build a declarative schema enforcement engine with type casting, required checks, enum validation, custom async validators, and default values.
MongoDB: Keyset Cursor-Based Pagination & Sorting Engine
Implement high-performance cursor pagination with base64 token encoding, avoiding offset skip() performance degradation on large collections.