Answer
Synchronous DOM updates block rendering. Asynchronous updates use Promises or requestAnimationFrame to avoid UI jank.
Quick Answer
Synchronous DOM manipulation (direct writes) blocks rendering — the browser can't paint until the JS finishes. Asynchronous DOM manipulation (via requestAnimationFrame or setTimeout(0)) defers the change to the next paint cycle, keeping the UI responsive. For smooth animations, always use requestAnimationFrame — it's synchronized with the browser's display refresh rate.
S
SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ