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By default an experiment fires as soon as the page has matched Location and Audience rules. That is fine for most tests. It is wrong for a few. An activation trigger shifts the moment of exposure. Instead of the page load itself, the trigger decides when the visitor counts as “in the test” and when the variant’s JavaScript runs. That timing lands in your funnel numbers, so it matters.

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The four modes

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Why not just fire on load

Because a visitor who never reached your CTA is not part of a CTA test. Counting them dilutes both arms equally, but it also shows a much lower “conversion rate” than the number your funnel already shows, and stakeholders notice. Two examples: A hero-CTA experiment on a long landing page. If it fires on load, the visitor counts even if they bounced from the fold. Switch to When visible on the CTA’s own element, and the visitor only counts when the CTA scrolled into view. An “upgrade” modal that shows on a specific click. If it fires on load, every page visitor is in the test, but only a small fraction ever see the modal. Switch to On click on the trigger button, or Manual if you open the modal from your own code.

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On click

Pick a CSS selector. Any click that matches, via event.target.closest(selector), activates the experiment.
  • ABTestly installs a single passive capturing click listener per site and dispatches to the right selectors from there. It does not fight your handlers.
  • Both arms, control and variant, activate on the click. That is how you keep the two sides comparable.
  • If nothing on the page matches your selector when the page loads, ABTestly logs a debug event so you can catch selector typos in preview.

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When visible

Pick a CSS selector. When an element matching that selector is at least 1 % on-screen, the experiment activates.
  • Uses one IntersectionObserver per experiment. It is a browser API, cheap.
  • Fires once per visitor per experiment per pageview. A visitor who scrolls past the element and back does not re-activate.

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Manual

Sometimes the moment you want to count is inside code you already write. step three of a wizard, the point after a form’s validation succeeds, the opening of a modal. Call:
Return values (for dev.apply diagnosis, not typical use): The key is the experiment’s short code (ABTESTLY_EXP_KEY), not its UUID or its display name. You can find it on the experiment detail page next to the name.

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SPA behaviour

On a single-page app route change, ABTestly clears the current route’s pending activation registrations and re-arms triggers for the eligible experiments on the new route. In practical terms: your click and visibility triggers behave the same on route two as they did on route one, without you doing anything special.

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Exclusion groups and activation

An experiment in an exclusion group cannot also use an activation trigger, the editor disables the field. Exclusion group members are decided at page load; deferring the decision to a click or a manual call would break the guarantee that at most one member ever matches a given visitor.

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The screen

Activation section with mode picker

Activation section inside the experiment editor.