#JavaScript

Stop fighting CORS. Understand preflight requests, credentials, wildcard mistakes. CORS isn't a bug—it's your API warning you about real security issues.

ERR_REQUIRE_ESM. Missing extensions. No __dirname. The ESM/CJS war is still breaking Node.js projects in 2026. Here's the root cause, all five errors you'll hit, and the exact fixes for each one.

Every JavaScript developer has written await Promise.all(items.map(async item =>...)). It works — until you hit a rate-limited API, a paginated async generator, or a ReadableStream. Array.fromAsync() is the purpose-built replacement you didn't know you needed.

You changed assert to with and everything worked again — but you have no idea why the syntax changed, whether it's safe to use, or what happens in environments that still expect assert. Here's the full story, the exact migration, and every edge case that will trip you up.

You open DevTools, check the console, inspect an element, close it. But DevTools is not a debugger — it's a full developer environment. Here's the power you're leaving on the table.