Experimentation that actually works with Single Page Applications
Single Page Applications are fast — but most A/B testing tools were built for multi-page websites.
That’s why SPAs often suffer from late bucketing, visual flicker, hydration issues, and “who loaded first” bias.
Conversion Workers solves this by making the experiment decision before your app renders —
so the user sees the right experience from the first paint, and your data stays clean.
Zero-flicker experiences
Users see the correct version immediately — no “swap after load”, no layout jumps, no awkward flashes. Great for high-visibility components like pricing, navigation, checkout and onboarding.
Cleaner results (no hidden bias)
Assignment happens before rendering, so results aren’t skewed by late bucketing, slow devices, race conditions, or “who hydrated first”.
Works with client-side routing
Users stay consistently in A or B across in-app navigation. No re-bucketing, no “route changed so the test broke”, no fragile event wiring.
Less code in your app
Keep experiments governed centrally at the edge. Avoid scattering conditional logic and test flags throughout your application codebase.
Test “new app” experiences safely
Serve alternative routes or swap bundles to deliver genuinely different SPA experiences — without rebuilding pages via tag-based DOM manipulation.
Predictable governance
Rules, targeting and rollout are controlled in one place. Roll back instantly without redeploying the app or waiting for a release train.
How Conversion Workers supports SPAs
The trick with SPAs is simple: make the decision before the app loads, then keep the user consistent as they navigate client-side.
When a user first hits a route, Conversion Workers evaluates targeting rules and assigns a variant before any app code executes.
A lightweight cookie keeps the user in the same version across navigation, sessions and refreshes — so the experience stays coherent.
The edge can serve variant experiences using proven delivery techniques that don’t rely on brittle “DOM surgery” after load.
Two SPA-friendly delivery options
Most SPA testing problems come from trying to change the page after the application has started. Conversion Workers avoids that by delivering the correct experience from the beginning.
Keep the URL stable, change the experience
Users request a normal route, but Conversion Workers can serve an alternative version behind the scenes. This is ideal when you want a clean separation between Control and Variant.
- Same public URL, different underlying version
- Great for landing pages, pricing, onboarding, checkout entry
- Compatible with server-rendered and client-rendered apps
Boot a different SPA without redirects
For large applications, the most robust approach is to swap which app bundle is loaded for a user, based on their assigned variant.
- Same route, different bundle — perfect for client-side routing
- No flicker because the app starts in the right version
- Ideal for major UI changes and “v2 experience” tests
SPA FAQ
Common questions from teams running modern web applications.
Will this work if my app navigates without full page loads?
Yes. Conversion Workers assigns the user on entry, then keeps the assignment consistent while the app navigates client-side. The experience remains stable across the journey.
Do we need to add code into the app?
Often, no. Many SPA experiments can be delivered entirely at the edge (serving alternate routes or swapping bundles). If needed, a lightweight config flag can be injected — but the goal is to keep your app clean.
What about performance?
Because decisions are made at the edge, you avoid running heavy client-side experiment code. That typically means fewer layout shifts, faster first paint, and a smoother user experience.
How do I run “big change” tests safely?
Use bundle swaps or alternate routes. This lets you ship a genuinely different experience without relying on fragile, after-load DOM manipulation — and you can roll back instantly if needed.