Quick Reference
| Need | See |
|---|---|
| HTML/CSS issues | html-css.md |
| JavaScript patterns | javascript.md |
| React/Next.js/frameworks | frameworks.md |
| Deploy to production | deploy.md |
| Performance/SEO/a11y | performance.md |
Critical Rules
- DOCTYPE matters — Missing
<!DOCTYPE html>triggers quirks mode; layouts break unpredictably - CSS specificity beats cascade —
.classoverrides element selectors regardless of order ===not==— Type coercion causes"0" == falseto be true- Async/await in loops —
forEachdoesn't await; usefor...oforPromise.all - CORS is server-side — No client-side fix; configure
Access-Control-Allow-Originon the server - Responsive = viewport meta — Without
<meta name="viewport">, mobile renders desktop-width - Form without
preventDefault— Page reloads; calle.preventDefault()in submit handler - Images need dimensions — Missing
width/heightcauses layout shift (CLS penalty) - HTTPS or blocked — Mixed content (HTTP resources on HTTPS pages) gets blocked by browsers
- Environment variables leak —
NEXT_PUBLIC_*exposes to client; never prefix secrets
Common Requests
"Make it responsive" → Mobile-first CSS with media queries; test at 320px, 768px, 1024px
"Deploy to production" → See deploy.md for Vercel/Netlify/VPS patterns
"Fix CORS error" → Server must send headers; proxy through same-origin if you can't control server
"Improve performance" → Lighthouse audit; focus on LCP, CLS, FID; lazy-load below-fold images
"Add SEO" → Title/description per page, semantic HTML, OG tags, sitemap.xml
Framework Decision Tree
- Static content, fast builds → Astro or plain HTML
- Blog/docs with MDX → Astro or Next.js App Router
- Interactive app with auth → Next.js or Remix
- Full SSR/ISR control → Next.js
- Simple SPA, no SEO needed → Vite + React/Vue