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Troubleshooting

When to Use

You're experiencing HTMX issues and need to diagnose and fix them.

Common Issues and Solutions

Issue: HTMX attributes not working

  • Check library attachment: 

    # View page source, search for htmx
# Should see: <script src="/core/assets/vendor/htmx/htmx.min.js">

  • Verify attributes rendered: 

    # Inspect element in browser DevTools
# Should see: data-hx-get="/path" data-hx-target="#id"

  • Confirm Htmx::applyTo() called: 

    $htmx = new Htmx();
$htmx->get($url)->target('#content');
$htmx->applyTo($build['element']);  // REQUIRED

Issue: Content not swapping

  • Verify target exists: 

    // Browser console
document.querySelector('#target-id');  // Should not be null

  • Check select selector matches response: 

    // Response must contain element matching select attribute
(new Htmx())
  ->select('#main-content')  // This must exist in response
  ->target('#wrapper')
  ->applyTo($build);

  • Inspect Network tab: 

    # DevTools Network tab → Click request
# Preview tab → Verify content present
# Headers tab → Verify HX-Request: true

  • Verify HtmxRenderer invoked: 

    # Response should be minimal HTML structure, not full page
# Look for: <!doctype html><html><head><meta name="robots" content="noindex">

Issue: JavaScript not executing on swapped content

  • Check behavior implementation: 

    Drupal.behaviors.myBehavior = {
  attach(context, settings) {
    // Use context, not document
    $(context).find('.my-element').once('myBehavior').each(function() {
      // Your code
    });
  }
};

  • Verify htmx:drupal:load fires: 

    // Browser console
htmx.on('htmx:drupal:load', (e) => console.log('Load event', e.detail));

  • Check asset loading: 

    // Browser console
htmx.on('htmx:beforeSwap', (e) => console.log('Assets:', e.detail));

Issue: Form not submitting

  • Verify form method: 

    (new Htmx())
  ->post($url)  // Must match form method
  ->applyTo($form['submit']);

  • Check CSRF token present: 

    # View form source
# Should have: <input type="hidden" name="form_token">
# Drupal forms include this automatically

  • Validate route exists: 

    drush route:debug | grep my_route

Issue: Multiple swaps not working

  • Use swapOob: 

    // Response element needs OOB attribute
(new Htmx())
  ->swapOob('true')
  ->applyTo($form['status'], '#wrapper_attributes');

  • Verify IDs match: 

    // Page has: <div id="status">
// Response must have: <div id="status" data-hx-swap-oob="true">

Issue: Browser history not updating

  • Use pushUrlHeader: 

    (new Htmx())
  ->pushUrlHeader(Url::fromRoute('my.route', ['id' => $id]))
  ->applyTo($form);

  • Check history cleanup: 

    // Browser console → Network tab
// Click request → check if _wrapper_format in URL
// Should be removed before history save

Debugging HTMX Requests

Browser DevTools Network Tab:

  1. Filter by XHR
  2. Click HTMX request
  3. Headers tab:
  4. Request Headers: HX-Request: true, HX-Target: #id, HX-Trigger: element-id
  5. Response Headers: HX-Push-Url, HX-Trigger, etc.
  6. Preview tab: See rendered HTML
  7. Response tab: See raw HTML

HTMX Event Logging:

// Add to browser console for debugging
htmx.logAll();

// Or specific events
htmx.on('htmx:beforeRequest', (e) => console.log('Request:', e.detail));
htmx.on('htmx:afterSwap', (e) => console.log('Swapped:', e.detail));
htmx.on('htmx:responseError', (e) => console.error('Error:', e.detail));
htmx.on('htmx:drupal:load', (e) => console.log('Drupal loaded:', e.detail));

Reference: HTMX Events

Server-Side Debugging:

// Check if request is HTMX
if ($this->isHtmxRequest()) {
  \Drupal::logger('my_module')->notice('HTMX request detected');
  \Drupal::logger('my_module')->notice('Trigger: @trigger', [
    '@trigger' => $this->getHtmxTriggerName(),
  ]);
}

// Dump render array before returning
\Drupal::logger('my_module')->debug('Build: @build', [
  '@build' => print_r($build, TRUE),
]);

// Verify route option
$route = \Drupal::routeMatch()->getRouteObject();
$htmx_route = $route->getOption('_htmx_route') ?? FALSE;
\Drupal::logger('my_module')->notice('HTMX route: @option', [
  '@option' => $htmx_route ? 'TRUE' : 'FALSE',
]);

Check HtmxRenderer Invocation:

# View response HTML source
# Should see minimal structure:
<!doctype html>
<html>
<head>
<meta name="robots" content="noindex">
<title>...</title>
...
</head>
<body>
<!-- Status messages -->
<!-- Main content -->
</body>
</html>

# NOT full page with header, footer, sidebars, etc.

Common Mistakes

  • Not checking browser console for JavaScript errors — Errors break HTMX processing
  • Assuming HTMX request without checking — Use isHtmxRequest() to verify
  • Not using htmx.logAll() for debugging — Visibility into lifecycle is critical
  • Forgetting to clear cache after code changes — Routing and render changes require cache rebuild
  • Not testing in multiple browsers — Some behaviors vary by browser
  • Debugging in production — Use local/dev environment with debugging enabled

See Also