ntb

Use it

const variant = ntb('hero');      // 0 or 1, sticky for this browser
if (variant === 1) document.body.classList.add('hero-b');

ntb('cta-copy', 3);               // three-way test → 0, 1, or 2

Assignment is uniform random, persisted in localStorage under ntb:<test>. The exposure fires once per test per page load — SPA route changes don't re-fire it. Analyze by unique visitors per variant, not raw events.

Where exposures land

• GA4 — dataLayer.push({event: 'ab_assigned', ntb_test, ntb_variant}), readable by gtag.js and GTM. Register the two params as custom dimensions to report on them.
• Umami — umami.track('ab_assigned', {test, variant}), with a short poll so a deferred Umami script still catches the event.
• umami-shopify — Shopify.analytics.publish('umami:ab', {test, variant}); the custom pixel forwards each publish to Umami as one ab_assigned event, sequenced after the pageview.