Interview Questions
Promises provide structured handling of asynchronous operations with chaining capabilities and built-in error handling through .then() and .catch(). Unlike callbacks, which can lead to callback hell, Promises enable cleaner code organization and better error propagation. Promises are preferred for modern asynchronous operations, while callbacks remain relevant for event handling and legacy code integration. Consider error handling requirements and code maintainability when choosing between them.
async/await provides synchronous-looking code for asynchronous operations, improving readability and maintainability. async functions automatically return Promises, and await pauses execution until Promises resolve. However, they can't be used in regular functions or at the top level (pre-ES modules). Error handling requires try/catch blocks, and parallel execution needs careful consideration. Consider performance implications and proper error handling strategies when using async/await.
Promise.all() handles multiple concurrent Promises, resolving when all complete. Promise.race() resolves with the first completed Promise. Promise.allSettled() waits for all Promises regardless of success/failure. Promise.any() resolves with first successful Promise. Consider error handling, timeout implementation, and performance optimization when working with multiple Promises. Implement proper cleanup for rejected Promises.
Use Promise catch() blocks or try/catch with async/await. Implement proper error propagation and recovery strategies. Handle both synchronous and asynchronous errors appropriately. Consider error types and appropriate responses. Implement logging and monitoring for asynchronous errors. Ensure proper cleanup on error conditions.
The event loop manages execution of asynchronous operations by processing the call stack, callback queue, and microtask queue. Microtasks (Promises) have priority over macrotasks (setTimeout, setInterval). Understanding the event loop is crucial for performance optimization and preventing blocking operations. Consider task prioritization and proper sequence handling.
Implement proper synchronization mechanisms using Promise.race() or flags. Handle out-of-order responses appropriately. Consider cancellation patterns and cleanup. Implement proper state management for concurrent operations. Document race condition handling strategies. Test edge cases thoroughly.
Use Promise.race() with timeout Promise, or implement custom timeout logic. Handle cleanup for timed-out operations. Consider appropriate timeout durations and retry strategies. Implement proper error messaging for timeouts. Handle partial completions appropriately. Document timeout behavior and recovery procedures.
Use finally blocks or cleanup functions in Promise chains. Implement proper cancellation patterns. Handle resource release in error cases. Consider memory management and leak prevention. Document cleanup requirements and procedures. Implement proper error handling during cleanup.
Return values from then() handlers for proper chaining. Implement proper error handling at each step. Consider Promise flattening and composition. Handle side effects appropriately. Document chain dependencies and requirements. Implement proper cleanup in chain breaks.
Implement exponential backoff strategy. Handle maximum retry attempts. Consider error types for retry decisions. Implement proper timeout handling. Document retry behavior and limitations. Handle permanent failures appropriately. Consider resource implications of retries.
Use Promise.all() for parallel execution, implement proper rate limiting. Handle partial failures appropriately. Consider dependency order and prioritization. Implement proper error aggregation. Document concurrency limitations and requirements.
Use AbortController for fetch requests, implement custom cancellation tokens. Handle cleanup on cancellation. Consider partial completion handling. Implement proper state management. Document cancellation behavior and limitations.
Async iterators enable asynchronous iteration using for-await-of. Async generators combine generator and async functionality. Handle proper error propagation. Consider memory usage and cleanup. Document iteration behavior and requirements. Implement proper cancellation.
Implement proper cleanup of event listeners and subscriptions. Handle reference cleanup in closures. Consider weak references when appropriate. Implement proper cancellation patterns. Monitor memory usage. Document cleanup requirements.
Implement proper loading states and dependencies. Handle initialization errors appropriately. Consider lazy initialization patterns. Document initialization requirements and sequence. Implement proper cleanup on failed initialization.
Use closures to manage timing. Implement proper cleanup of timers. Consider immediate execution options. Handle edge cases appropriately. Document timing behavior and requirements. Implement proper cancellation.
Use async test frameworks. Implement proper assertions for async results. Handle timeout and error cases. Consider test isolation and cleanup. Document test requirements and assumptions. Implement proper mock timing.
Consider event order and timing. Handle proper error propagation. Implement cleanup on handler removal. Consider memory implications. Document handler behavior and requirements. Implement proper state management.
Handle concurrent execution limits. Implement proper queue management. Consider priority handling. Handle error cases appropriately. Document queue behavior and limitations. Implement proper cleanup.
Implement proper loading and error states. Handle race conditions appropriately. Consider optimistic updates. Implement proper cleanup on state changes. Document state transitions and requirements. Handle edge cases.
Implement proper fallback mechanisms. Handle partial failures appropriately. Consider retry strategies. Document recovery procedures and limitations. Implement proper state restoration. Handle cleanup during recovery.
Handle async context preservation. Implement proper error tracking. Consider performance impact. Document logging requirements and format. Implement proper cleanup of log resources. Handle sensitive data appropriately.
Implement proper dependency resolution. Handle circular dependencies appropriately. Consider initialization order. Document dependency requirements and limitations. Implement proper cleanup. Handle dependency failures.
Implement proper concurrency control. Consider caching strategies. Handle batch operations appropriately. Document performance requirements and limitations. Implement proper monitoring. Handle resource constraints.
Implement proper backpressure handling. Consider memory usage and buffering. Handle error propagation appropriately. Document stream behavior and limitations. Implement proper cleanup. Handle partial processing.
Handle error propagation appropriately. Implement proper recovery mechanisms. Consider error scope and isolation. Document error handling requirements. Implement proper cleanup. Handle nested errors.
Implement proper initialization and cleanup. Handle event order appropriately. Consider dependency management. Document lifecycle requirements. Implement proper error handling. Handle partial completion.
Handle error context preservation. Implement proper error aggregation. Consider error categorization. Document reporting requirements. Implement proper cleanup. Handle sensitive information appropriately.
Document async behavior and requirements clearly. Consider error cases and handling. Document cleanup requirements. Implement proper examples and usage patterns. Consider versioning and compatibility. Handle API documentation appropriately.