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How to run A/B tests in Bubble

Jan 11, 2024

Bubble is a great tool for building marketing websites. However, sometimes you may be unsure if a change actually improves your conversion rate. This is where A/B testing is helpful. It enables you to test and compare the results of your changes.

This tutorial shows you how to set up A/B tests with Bubble and PostHog to get the most out of your website.

1. Add PostHog to your Bubble site

First, sign up to PostHog. Then, go to your project settings and copy your web snippet. It looks like this:

!function(t,e){var o,n,p,r;e.__SV||(window.posthog=e,e._i=[],e.init=function(i,s,a){function g(t,e){var o=e.split(".");2==o.length&&(t=t[o[0]],e=o[1]),t[e]=function(){t.push([e].concat(,0)))}}(p=t.createElement("script")).type="text/javascript",p.async=!0,p.src=s.api_host+"/static/array.js",(r=t.getElementsByTagName("script")[0]).parentNode.insertBefore(p,r);var u=e;for(void 0!==a?u=e[a]=[]:a="posthog",u.people=u.people||[],u.toString=function(t){var e="posthog";return"posthog"!==a&&(e+="."+a),t||(e+=" (stub)"),e},u.people.toString=function(){return u.toString(1)+".people (stub)"},o="capture identify alias people.set people.set_once set_config register register_once unregister opt_out_capturing has_opted_out_capturing opt_in_capturing reset isFeatureEnabled onFeatureFlags getFeatureFlag getFeatureFlagPayload reloadFeatureFlags group updateEarlyAccessFeatureEnrollment getEarlyAccessFeatures getActiveMatchingSurveys getSurveys onSessionId".split(" "),n=0;n<o.length;n++)g(u,o[n]);e._i.push([i,s,a])},e.__SV=1)}(document,window.posthog||[]);

With the snippet copied, go to your Bubble site settings by clicking on the icon in the left-hand menu. If you haven’t already, sign up for at least the Starter site plan. This enables you to add custom code.

Go to the SEO / metatags tab in site settings. Paste your PostHog snippet in the Script/meta tags in header section. Then, deploy your site to live.

2. Capture a custom event

We're going to create an A/B test comparing how a button's text affects its click-through rate. To compare the results, we first capture a custom event and then set it as our goal metric for our A/B test.

To capture this event:

  1. Install the Bubble Toolbox plugin. This enables us to run custom JavaScript code when the button is pressed.

  2. Add a new button to your Bubble site. Click on the button and then on Add workflow in the popup menu.

  3. Click on add an action. In the menu that appears, click on Plugins and then Run javascript. This will open a new menu where you can add JavaScript code.

  4. Add the following code under the Script heading:


Finally, deploy your changes to live and then click your new button to see the event in PostHog.

Events captured in PostHog

3. Create an A/B test in PostHog

If you haven't done so already, you'll need to upgrade your PostHog account to include A/B testing. This requires entering your credit card details, but don't worry, we have a generous free tier of 1 million requests per month – so you won't be charged anything yet.

Next, go to the A/B testing tab and create an A/B test by clicking the New experiment button. Add the following details to your experiment:

  1. Name it "Bubble button experiment".
  2. Set "Feature flag key" to bubble-button-experiment.
  3. Under the experiment goal, select the ab_test_button_clicked event we created in the previous step.
  4. Use the default values for all other fields.

Click "Save as draft" and then click "Launch".

Experiment setup in PostHog

4. Implement the A/B test in Bubble

The final step is to add the experiment code in Bubble. We need to add code that does the following:

  1. Fetch the bubble-button-experiment flag.
  2. Change the title of the button based on whether the value of the flag is control or test.

To do this, we add another workflow event. Go to the Workflow tab in Bubble. Create a new Page is loaded event with an action to run custom JavaScript code (like we did for capturing our custom event).

Use the following code to change the title of the button based on the value of the feature flag:

posthog.onFeatureFlags(() => {
// Find the button you'd like to change. In our case, we change the text of the "Sign Up" button
var button = Array.from(document.querySelectorAll('button')).find(el => el.textContent === 'Sign Up');
if (button) {
const flagValue = posthog.getFeatureFlag('bubble-button-experiment')
if (flagValue === 'control') {
button.textContent = "This is the title for CONTROL group"
} else if (flagValue === 'test') {
button.textContent = "This is the title for TEST group"

Finally, deploy your changes to live.

That's it! Your A/B test is now live. PostHog will split your users so half see the updated button text and tracks whether it has an impact on your click-through rate. You can view your test results on the experiment page in PostHog.

If you want to test each variant of your experiment to make sure it is working correctly, add the line posthog.featureFlags.override({'bubble-button-experiment': 'variant_name'}) to your code:

posthog.onFeatureFlags(() => {
// Override the feature flag
posthog.featureFlags.override({'bubble-button-experiment': 'test'}) // or 'control'
// rest of your code...

Further reading