onFormieInit event not working in Safari

[anita-chouhan]

Describe the bug

We are using onFormieInit to attach a function to Formie initialisation. It is failing on Safari.

Sample code

(function (window) {
document.addEventListener('onFormieInit', (e) => {
    // The instance of the Formie JS library
    let Formie = e.detail.formie;
    console.log(Formie);

    // The `<form>` HTML element
    let $form = e.detail.$form;
    console.log($form);

    // The instance of the Formie form class, which encapsulates most logic
    let form = e.detail.form;
    console.log(form);

    // The `formId` of the form, used as a unique identifier
    let formId = e.detail.formId;
    console.log(formId);

  });
})(this);

Steps to reproduce

1. Add an event listener for Formie.
2. Test the console logs on Safari version 26.5.

Form settings

• Multi-page form: No
• Submission Method: Ajax
• Client-side Validation: Yes
• Custom Form Templates: No

Craft CMS version

5.9.16

Plugin version

3.1.16

Multi-site?

No

Additional context

It is working on certain versions of Firefox, Chrome and Safari.

[engram-design]

I have a feeling this might have something to do with Safari and IntersectionObserver for how we auto-initialize our JS for forms.

A quick diagnostic check you can do: in Safari, after page load, run window.Formie?.forms?.length in your browser console. If it’s 0, it's an observer issue. If it’s 1+, the event fired before your listener was registered.

I have also made some tweaks for Safari that might also help. It'll be worth checking on your end if you can.

To get this early, run composer require verbb/formie:"dev-craft-5 as 3.1.27".