FrontendHaltPerformance·Intermediate·Conceptual·1 min read
What is input delay and what causes it?
Short interview answer
It's the gap between the interaction happening and the event handler starting to run, caused by the main thread being busy with another task — a long render, parsing, a timer callback — that must finish first. Breaking up long tasks is the fix.
Key takeaway
Explain the underlying mental model clearly, then support it with a concrete example and its trade-offs.