Chapter 8: AJAX Divine Power - Change the page without breaking it

Practical Pitfalls

• Problem

  A hidden component never comes back after AJAX toggle.
  Cause

  No DOM placeholder exists while hidden, so AJAX has no update anchor.
  Solution

  Enable placeholder output for visibility-toggled components.
• Problem

  Change events never trigger server logic.
  Cause

  Event name does not match current Wicket expectations (legacy naming left behind).
  Solution

  Use version-correct event names and verify behavior after upgrades.
• Problem

  First click does nothing, second click works.
  Cause

  DOM/event conflicts or JavaScript errors interfere with behavior binding.
  Solution

  Check browser console, propagation path, and actual binding target first.
• Problem

  After session timeout, UI appears frozen.
  Cause

  AJAX call receives normal redirect handling, not AJAX-specific recovery flow.
  Solution

  Implement AJAX-aware timeout handling and route users back to login cleanly.
• Problem

  Users get stuck when stale page exceptions occur.
  Cause

  No user-facing recovery message or reload path is provided.
  Solution

  Catch and explain the state issue, then guide users to reload or retry safely.
• Problem

  Adding custom jQuery AJAX increases stale errors.
  Cause

  Custom calls hit Wicket-managed page URLs and break render count consistency.
  Solution

  Move custom calls to dedicated endpoints separated from page-state URLs.
• Problem

  jQuery plugins work on first render but fail after partial updates.
  Cause

  Plugin initialization is not re-run after DOM replacement.
  Solution

  Re-initialize plugins explicitly after AJAX updates.
• Problem

  Custom input components throw hierarchy/update errors in AJAX flows.
  Cause

  Disabled/hidden states remove expected update anchors.
  Solution

  Apply placeholder output rules consistently to custom components too.