Fix AJAX submission issues with multiple forms on same page

[wotis]

Problem Description

When using two forms via shortcode on the same page, AJAX submission can fail or hang at the "waiting" message. This issue is particularly evident when the first form is hidden due to time/date constraints while the second form is visible and being submitted.

Steps to Reproduce

1. Create two forms (e.g., with IDs 51 and 52)
2. Add both to a page using shortcodes: [cforms]51[/cforms] and [cforms]52[/cforms]
3. Configure first form with date/time restrictions so it's not displayed
4. Try to submit the second form via AJAX
5. Observe that the "waiting" message does not disappear

Root Cause

1. Orphaned HTML elements: Forms hidden by time constraints still create HTML message box elements (<div id="usermessage...a">) even though the form itself is not rendered
2. Missing AJAX error handling: No error handling for invalid responses or AJAX failures
3. JSON corruption: Additional output can corrupt JSON responses from the server

Changes Made

In lib_render.php (lines 116-123)

• Move cforms2_check_time() check before creating any HTML elements
• Prevents orphaned message boxes for forms that won't be displayed
• Remove duplicate time check logic later in the file

In lib_ajax.php (lines 20-23)

• Add ob_clean() to clear any previous output before sending JSON
• Ensures clean JSON responses without corrupted data

In js/cforms.js (lines 185-202)

• Replace jQuery.post() with jQuery.ajax() for better error handling
• Add response validation to check for valid JSON structure
• Add error handler for AJAX failures
• Use configured failure messages instead of technical error output

Testing

Tested with:

• ✅ Two forms (IDs > 50) on same page
• ✅ First form hidden by date restrictions
• ✅ Second form submits successfully via AJAX
• ✅ Error conditions handled gracefully with user-friendly messages
• ✅ Works with both forms visible
• ✅ Works with only one form visible

Impact

This fix ensures that:

• Multiple forms can coexist on the same page
• Time-restricted forms don't interfere with other forms
• AJAX errors are handled gracefully
• Users see configured error messages, not technical output
• Form submissions are reliable even under load

Affected Versions

• cforms2 version 16.0.1
• WordPress 5.2+
• Tested on IONOS hosting