Dom Performance
Testing & Qualitydom-performanceDom Performance is an Agent Skill for testing & quality published in the thedaviddias/Front-End-Checklist repository on GitHub: a SKILL.md instruction file an AI agent can load to do this task.
Use when reviewing scripts, client components, bundles, or runtime behavior related to Minimize costly DOM read/write operations. Inspect both source code and the browser execution path so fixes target the real bottleneck or bug. In React, repeated requestAnimationFrame-driven state updates across multiple mounted components are a valid performance smell when visible in the source.
How to use this skill
Bring this guide into your coding agent with a prompt tailored to the tool you use.
- Open your project in Codex.
- Copy and paste the prompt below.
- Review files and risks before approving any action.
Inspect the Agent Skill at https://github.com/thedaviddias/Front-End-Checklist/blob/HEAD/skills/dom-performance/SKILL.md and all supporting files. Report provenance, permissions, scripts, dependencies, and security risks. Propose an exact installation into .agents/skills/dom-performance, but wait for my approval before writing files or running scripts.
Copying this prompt does not install or run the skill. Review third-party files before use.
Minimize costly DOM read/write operations
Every time you read a layout property after making a DOM change, the browser must synchronously recalculate layout (reflow) before returning the value. Doing this in a loop — even with just 10 elements — can freeze the page for hundreds of milliseconds. This is called layout thrashing and is one of the most common causes of janky animations and slow renders.
Quick Reference
- Never interleave DOM reads (offsetHeight, getBoundingClientRect) with DOM writes (style changes)
- Batch all reads first, then all writes
- Use requestAnimationFrame for visual updates
- Use DocumentFragment or innerHTML for bulk DOM insertion
- Avoid per-frame React state updates across many visible components when a simpler CSS or reduced-frequency approach would work
- Use passive listeners for scroll, touch, and wheel when you do not call preventDefault
Check
Identify any layout thrashing in this code — places where DOM reads and writes are interleaved in loops. Also flag scroll, touch, and wheel listeners that should be passive to avoid blocking the main thread.
Fix
Refactor this code to batch all DOM reads before writes, eliminating forced synchronous layouts. Mark relevant listeners as passive when they do not need to cancel scrolling.
Explain
Explain layout thrashing, what causes it, and how batching reads and writes prevents it.
Code Review
Review scripts, client components, and browser execution paths related to Minimize costly DOM read/write operations. Flag exact imports, event handlers, runtime side effects, or blocking operations that violate the rule, and state how the change should be verified in the browser.
For full implementation details, code examples, and framework-specific guidance,
see references/rule.md.
Rule page: https://frontendchecklist.io/en/rules/javascript/dom-performance