[sebastianstein]

Problem

For forms with data-lux-form-identification="true" or "submitButton", LUX prevented the native submit and sent the form itself after 500 ms via form.submit() or submitButton.click(). The delay was there to keep the tracking request from being cancelled by the page navigation.

This conflicts with other scripts:

1. Double submit: If another script also takes over the submit, the form is sent twice. Example: powermail_cond ≥ 13.0.2. On in2code.de, every powermail submit with LUX enabled was stored, mailed and posted to Slack twice (see [BUGFIX] Prevent double submit when another script handles the submit powermail_cond#134).
2. Validation is bypassed: event.defaultPrevented was ignored. Forms that a JavaScript validation had stopped were still submitted after the delay.
3. Other submit handlers are skipped: form.submit() does not fire a submit event.

Solution

• true / submitButton: The form values are sent via navigator.sendBeacon() (same POST request as before). The native submit is not touched any more, so there is no delay.
• Fallback: If navigator.sendBeacon() is not available or can't queue the request (returns false, e.g. when the size limit is exceeded), the request is sent with the existing XHR (ajaxConnection()) instead.
• submitButton now behaves like true and is kept for backwards compatibility. The native submit includes the submitter, which was the reason for this mode (typo3/cms-form).
• preventDefault: unchanged. The submit is stopped, and the XHR with workflow callback still runs.
• Form conversions of A/B tests use the beacon as well.
• delaySubmit() and formDelayStop are removed. The documentation and TypoScript comments are updated.

Behaviour change

For true / submitButton, workflow responses of the formListeningRequest are not processed any more. Before, they could only run in the 500 ms before the page change. For workflows on submit, preventDefault is the documented way.

Tests (local LUX environment, Chrome, requests checked in the httpd access log)

Scenario	Before	After
true + another script prevents the submit and calls form.submit()	locally 1 POST, because the response came faster than the LUX delay. On in2code.de (slower response): 2 submits	1 form POST + beacon formListeningRequest, LUX no longer calls form.submit()
submitButton	not tested	1 POST without delay + beacon
true + validation blocks the submit	form sent anyway after the delay	not sent, values tracked
preventDefault	not sent, XHR + workflow callback	unchanged

• The rebuilt Lux.min.js / modern/chunks/Lux.mjs only contain this change: a rebuild of the unchanged source is identical to the committed files.
• make test-unit: 281 tests OK

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