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Younghoon Kim
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Younghoon Kim

I document what I learn while solving product problems with React and TypeScript.

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FRONTEND ENGINEERING NOTES

Engineering essays about the frontend.

React, TypeScript, Next.js, performance, testing, and source-code reading. I document what I learn in practice so the next decision is clearer.

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30 results

Latest essay

Does a global AGENTS.md really eat into the project-doc budget?

I understood project_doc_max_bytes to apply to the combined size of global and project documents, and wrote the same thing in my wiki. Measuring the model-visible prompt with codex debug prompt-input produced a different result. This post traces how I varied the limit, identified its scope, and retested the finding after the files changed.

Aug 15, 2026/9 min readaicodexagents-md

Browse essays

2026 / 73 posts
Jul 21Why I separated data processing and UI responsibilities from React Query custom hooksReact Query11 minJul 14I upgraded DOMPurify, so why did I end up fixing happy-dom?Testing17 minJul 09Why replacing window.confirm with a React Dialog is not just a UI swapReact11 min
2026 / 51 posts
May 26Why you should not start coding when you get a feature requestfrontend10 min
2026 / 32 posts
Mar 27Why should good tests make failures believable?Testing10 minMar 01useRef holds values not needed for rendering, so why should you not read it during render?React6 min
2026 / 24 posts
Feb 21Why is Next.js source code so complex? -- The cost of keeping Pages RouterNext.js7 minFeb 13Minor optimizations found in React source codeReact16 minFeb 10ESM is asynchronous, so how is static analysis possible?javascript8 minFeb 01Why Map and Set are known to have better performance than Arrayjavascript5 min
2026 / 11 posts
Jan 23Measure and improve the performance of the AI ​​tool you createdai4 min
2025 / 122 posts
Dec 20Why bundlers existbundler5 minDec 01Attaching a RAG-based AI chatbot to an open source document siteai7 min
2025 / 111 posts
Nov 01How does RSC split server/client bundles?Next.js4 min
2025 / 101 posts
Oct 27Measure, Compare, Decide - Filter Implementation Thought ProcessReact5 min