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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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26 results

Latest essay

1async function loadPosts(cursor?: string) {2 const res = await fetch('/api/posts')3 const json = await res.json()4 return json.posts as Post[]5}
app/blog/actions.ts

Why you should not start coding when you get a feature request

How do you handle vague requests like "make it faster" or "make it prettier"?

May 26, 202610 min readfrontendspec

Browse essays

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 / 105 posts
Oct 27Measure, Compare, Decide - Filter Implementation Thought ProcessReact5 minOct 12Server synchronization of the Local-First library: Connecting IndexedDB and React with useSyncExternalStore and memory cacheReact12 minOct 12CSR Revisited Solving Blank Screens: Prepaint's Snapshot Restoration and Stabilization JourneyReact14 minOct 11Making the CSR app's revisit experience more like SSR: From target redefinition to architectural transitionReact10 minOct 03React useState internal structure: secrets of functional updates and linked listsReact4 min

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Why you should not start coding when you get a feature request10 min leftWhy should good tests make failures believable?10 min read

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