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Props are read-only inputs passed from parent to child. State is mutable data managed inside the component itself. When state changes, React re-renders the component...
useEffect runs side effects after render. The dependency array controls when it re-runs: empty [] runs once on mount, [value] runs when value changes, omitted runs every render...
Reconciliation is React's algorithm for diffing the virtual DOM tree to determine the minimum number of DOM operations needed. React compares element type first, then props...
=== is strict equality — it checks both value and type without coercion. == is loose equality — it performs type coercion before comparison. Always prefer === in production code...
A closure is a function that retains access to its outer scope even after the outer function has returned. This enables data privacy and function factories...
The event loop is the mechanism that allows JavaScript to be non-blocking despite being single-threaded. It continuously checks the call stack and the task queue...
Start with requirements: read-heavy system, ~100M URLs stored, low latency reads. Use a hash function (base62) to generate short codes, store in a distributed DB with caching...
CAP states that a distributed system can only guarantee two of three: Consistency, Availability, and Partition tolerance. In practice, partition tolerance is mandatory...
A CDN is a globally distributed network of servers that caches and delivers content from the server closest to the user, reducing latency and load on the origin server...
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