Theme Compatibility & Advanced
Performance characteristics
Cart drawer JS size, lazy loading, and Web Vitals impact.
This article is a draft and may be incomplete or change before publishing.
Bundle size
Cart drawer JS is under 60KB gzipped. Tiny by modern standards — fast to download, fast to parse.
Lazy loaded
Nothing fetched until the cart actually opens. The drawer's JS doesn't run on page load — it's deferred until a customer triggers an open. Your homepage, PDP, and collection pages render at full speed without the drawer's overhead.
Web Vitals
Real-user Web Vitals (LCP, CLS, FID) on the cart drawer are tracked under Analytics → Web Vitals. Use this to monitor your real performance impact, not synthetic Lighthouse scores.
What can affect performance
- Custom HTML / CSS — Heavy injections can slow the drawer's first render.
- Large hero images — Recommendations or upsell hero images that aren't optimized.
- Slow theme — If your theme already has performance issues, the drawer can amplify them.
If LCP is high
Reduce hero image size, disable auto-open animation, or cut custom CSS injection. See the Web Vitals tracking article for the full guide.