fix(modal-checkout): return array when getting event handlers

[miguelpeixe]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

When getting the event handlers to be used here:

newspack-blocks/src/modal-checkout/index.js

Lines 469 to 473 in b828743

	// Remove default form event handlers.
	originalFormHandlers = getEventHandlers( $form[ 0 ], 'submit' ).slice( 0 );
	originalFormHandlers.forEach( handler => {
	$form.off( 'submit', handler.handler );
	} );

The function can return undefined if the element has events but not the event being requested. It's a rare edge case only seen in a race condition, where a click event handler is registered, but no submit event handler has been registered yet.

This crashes the code above with Uncaught TypeError: Cannot read properties of undefined (reading 'slice').

How to test the changes in this Pull Request:

1. While on the release branch, tweak lines 219-225 of src/modal-checkout/index.js to run behind setTimeout:

setTimeout(() => {
  setEditingDetails( true );
  if ( ! $gift_options.length ) {
    // Perform initial validation so it can skip 1st step if possible.
    validateForm( true, setReady );
  } else {
    setReady();
  }
}, 10);

2. Start the modal checkout as an anonymous user (register a new reader in the process if your site requires you to)
3. If the checkout doesn't crash, try again or tweak the timeout delay until you hit it. Mine was 10, but also intermittent.
4. Checkout this branch, reapply the setTimeout, and confirm that there's no crash when there are event handlers but none in the submit event
5. Complete the checkout flow and confirm it behaves as expected

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?

[claudiulodro]

I wasn't able to replicate the race condition failure locally, so not sure if you want a second opinion, but I can confirm that Checkout works fine with this PR and the code change doesn't seem to be doing anything unreasonable. :)

[matticbot]

🎉 This PR is included in version 4.14.3 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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