Caches, CDNs and why updates 'don't show'

Most of the web's speed comes from copying things closer to you — and most 'my update isn't live' panic comes from those copies not being thrown away.

The four caches, near to far

• Browser cache — files your browser stored on disk with the response (often for a year, for hashed assets).
• Service worker — a script that can serve your whole app offline (this is how PWAs work).
• CDN edge — servers worldwide holding copies of the site's static files.
• Server-side cache — pre-computed pages the backend reuses instead of rebuilding.

That's why asset files get hashed names (app-Dx8f2.js): change the file, the name changes, every cache treats it as brand new. When a site update 'doesn't show', a stale cache somewhere is the usual suspect — a hard refresh or cache-busting deploy fixes it.