FrontendHaltPerformance·Intermediate·Conceptual·1 min read
What causes CLS?
Short interview answer
Images or embeds without reserved space, injected content above existing content, late font metric changes, and layout-changing animations. User-initiated shifts within the allowed window are treated differently, but the UI should still avoid surprise.
Key takeaway
Explain the underlying mental model clearly, then support it with a concrete example and its trade-offs.