My Voice, My Space

A small set of technical posts in English, translated/adapted from the main (Korean) blog. Read the full blog in Korean →

Latest posts

NewBackend API Design HTTP

Designing API Error Responses: Unifying Inconsistent Errors with RFC 9457 Problem Details

If one API returns a string, another returns { error }, and a third returns { message, code }, the frontend needs different code for every error. What makes a good error response, the standard RFC 9457 Problem Details format, per-field validation errors, hiding internals, and handling it all in one place in Node.js.

2026.10.0810 min read

Backend HTTP Web Security Node.js

CORS Errors Explained: Why Requests Get Blocked and How to Fix Preflight and Credentials Correctly

A 'has been blocked by CORS policy' error comes from the browser, not the server. The same-origin policy, simple vs preflighted requests, requests with cookies, and exposing response headers, verified in a real browser, plus why fixes like mode: 'no-cors' don't work.

2026.10.0812 min read

Frontend CSS

A Practical Guide to the CSS :has() Selector: Selecting Parents Without JavaScript

Cards that highlight when checked, forms that react as a whole to a bad input, star ratings that fill the stars before the one you hover. Things that used to need JavaScript, done with a single CSS :has() rule, with interactive examples.

2026.10.0810 min read

Frontend HTML

Things HTML Can Do Without JavaScript: Stop Building Everything Out of divs

Accordions, popovers, modals, autocomplete, form validation, and lazy-loaded images. A guide to the features you get from plain HTML tags and attributes, no library required. Less code, and accessibility comes for free.

2026.10.0813 min read

Backend HTTP Vercel

Using HTTP Caching Correctly: Cache-Control, ETag, and no-cache vs no-store

no-cache doesn't mean 'don't cache.' How max-age, no-cache, no-store, s-maxage, and immutable actually behave, checked by counting how many requests reach the server from a real browser, plus ETag and 304, old files showing up after a deploy, and Vercel's CDN cache.

2026.10.0810 min read

Backend HTTP API Design

Using HTTP Status Codes Correctly: 400 vs 422, 401 vs 403, and 200 vs 201 vs 204

If your errors come back as 200 with success: false, clients and monitoring tools can't tell anything failed. Which status code fits which situation, the difference between easily confused codes like 401 and 403 or 400 and 422, and the redirect trap where 301 turns POST into GET.

2026.10.0812 min read

Frontend JavaScript

Handling Async Errors in JavaScript Correctly: From What try/catch Misses to Promise.all vs allSettled

You wrapped it in try/catch and the error still escapes; the server returned 404 and fetch says it succeeded. The traps of async error handling: try/catch without await, return vs return await, fetch's res.ok, Promise.all vs allSettled, await in loops, and timeouts and cancellation, with a runnable demo.

2026.10.0811 min read

Concepts JavaScript Node.js

The JavaScript Event Loop Explained: How Microtasks and Macrotasks Are Ordered

Why does Promise.then run before setTimeout(0)? A walkthrough of the call stack, task queue, and microtask queue with runnable examples, plus how browsers and Node.js differ and how to keep long work from freezing the UI.

2026.10.0810 min read

Frontend JavaScript

JavaScript Higher-Order Functions Explained: From map, filter, and reduce to Building once and memoize

Functions that take functions or return functions. How to use map, filter, and reduce well, how to build practical higher-order functions like once, memoize, pipe, and curried helpers yourself, and traps like ['1','2','3'].map(parseInt).

2026.10.0812 min read

Frontend JavaScript

JavaScript ?? vs ||: How to Handle null, undefined, 0, and Empty Strings Correctly

Volume 0 turning into 50 and an empty nickname becoming 'Anonymous' are usually caused by ||. The difference between ?? and ||, optional chaining with ?., ??=, when default parameters actually apply, and the right way to check for null, with an interactive demo.

2026.10.089 min read