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169 questions
Start with the problem, evaluate alternatives, validate the technology with a small experiment and explain how you managed adoption and risk.
Explain how you identified what the developer needed, coached rather than simply solved the problem, and measured their progress.
Take heap snapshots in Chrome DevTools before and after the suspect action, compare what grew, and fix the retaining reference, which is usually a forgotten listener, timer, global variable or unbounded cache.
A component re-renders when its state changes, its parent re-renders, or a context it consumes changes; you prevent wasted renders by moving state down, using React.memo, and keeping props referentially stable.
Measure first with the Profiler and Lighthouse, then reduce unnecessary renders, split code with lazy loading, virtualise long lists, and optimise images and bundle size.
Core Web Vitals are Google鈥檚 field metrics for real-user experience: LCP (loading), INP (interactivity) and CLS (visual stability). They influence search ranking and are measured on real devices, not only Lighthouse.
Mapped types build a new object type by looping over keys (`{ [K in keyof T]: ... }`). Conditional types pick a result with `T extends U ? X : Y`, which is how many utility types are implemented.
Keep the main thread free by moving CPU-heavy work to worker threads or a job queue, and scale across cores and machines by running multiple processes (cluster or PM2) behind a load balancer with shared, external state.
Isolation levels (Read Uncommitted, Read Committed, Repeatable Read, Serializable) control how much concurrent transactions can see of each other's changes, trading consistency against concurrency to prevent dirty reads, non-repeatable reads and phantom reads.
Read the execution plan with EXPLAIN to find full scans and expensive joins, add or fix indexes for the filter and join columns, select only the columns and rows you need, and rewrite predicates so indexes can be used.
Use async all the way down instead of blocking on tasks with .Result or .Wait(), and in library code use ConfigureAwait(false) so continuations do not need to return to a captured context.
synchronized gives mutual exclusion and memory visibility for a block of code, while volatile only guarantees that reads and writes of one variable are visible to all threads and does not make compound operations such as count++ atomic.
The Global Interpreter Lock (GIL) in CPython lets only one thread execute Python bytecode at a time, so threads do not speed up CPU-bound code but still help with I/O-bound work.
Threading runs concurrent threads that share memory and suit blocking I/O, multiprocessing runs separate processes to use multiple CPU cores for CPU-bound work, and asyncio runs many non-blocking tasks cooperatively on one thread for high-volume I/O.
Generate a short unique code for each long URL (for example by base62-encoding a unique ID), store the mapping in a key-value or relational database, serve redirects through a cache because reads far outnumber writes, and record analytics asynchronously.
The CAP theorem says that during a network partition a distributed system must choose between consistency (every read sees the latest write) and availability (every request gets a response); you cannot have both while the partition lasts.
Replication copies the same data to several servers to improve read capacity and availability, while sharding splits the data across servers so each holds only a part, which increases write capacity and total storage.
Start with a well-structured monolith unless you have several teams and clear service boundaries, because microservices add distributed-system complexity such as network failures, data consistency and operational overhead.
Accept notification requests through an API, put them on a message queue, and let channel-specific workers (email, SMS, push, in-app) send them using user preferences, templates, retries with idempotency and rate limits.
Clients keep a persistent WebSocket connection to stateless chat servers; messages are stored durably, routed to the recipient鈥檚 server through a pub/sub layer, and delivered as push notifications when the recipient is offline.