Why We Rebuilt Our Magento Checkout with React: Performance Results

Magento's default Luma checkout loads a heavy Knockout.js stack, dozens of RequireJS modules, and payment iframes that fight for the main thread. For merchants where checkout is the conversion bottleneck, shaving seconds off load and interaction time pays back faster than another homepage hero image. We rebuilt checkout in React— React Checkout Pro —for Magento 2 and Hyvä stores that needed Shopify-like speed without leaving Adobe Commerce. Here is what we measured, what surprised us, and what we would do differently. The problem: checkout is where Core Web Vitals go to die Homepage optimizations are table stakes. Checkout is different: More JavaScript. Payment methods, validators, shipping step observers, and third-party scripts stack on one route. More layout shift. Address suggestions, shipping method lists, and tax updates re-render large DOM regions. More input delay. Autocomplete plugins, reCAPTCHA, and BNPL widgets compete on keydown handlers. On a representative Luma checkout (mid-size US retailer, ~80 SKUs in catalog, 4 payment methods), lab tests before migration showed: Metric Luma checkout (before) React checkout (after) LCP (lab, 4G) 4.8s 2.1s INP (field interaction) 320ms 95ms CLS (full flow) 0.18 0.04 JS transferred (checkout route) ~1.9 MB ~420 KB Time to interactive (est.) 6.2s 2.8s Field data from CrUX lagged lab wins by 4–6 weeks but trended the same direction once cache and CDN rules settled. Your numbers will differ. The pattern we see repeatedly: the biggest win is shipping less JavaScript to checkout , not micro-optimizing the JavaScript you keep. Architecture: React island, Magento brain We did not headless the entire storefront. Magento still owns: Quote totals and tax calculation Shipping rate requests Payment tokenization and order placement APIs Customer session and cart persistence React owns the UI layer: step navigation, form state, validation UX, and optimistic updates while Magento APIs catch up. High-level flow: Browser → React Chec