HTMX forms

Submit forms in your application without writing custom JavaScript using HTMX.

Before you start: add your site’s origin (e.g. https://example.com, plus your local dev URL such as http://localhost:5173) under your form’s Settings → Allowed Origins & Redirects. Browsers block fetch() responses from sites that aren’t listed. See Allowed Origins.

HTMX 2.0 Example

By default, HTMX 2.0 restricts requests to the same origin (selfRequestsOnly: true). Since Formkove’s API endpoint is hosted on https://app.formkove.com, you must configure HTMX to allow cross-origin requests, load the json-enc extension, and strip out any default HX- request headers to comply with CORS preflight policies.

HTML Form Code

<!-- Enable cross-origin requests for HTMX 2.0 -->
<meta name="htmx-config" content='{"selfRequestsOnly": false}'>

<!-- Load HTMX and the json-enc extension -->
<script src="https://unpkg.com/[email protected]/dist/htmx.min.js"></script>
<script src="https://unpkg.com/[email protected]/dist/ext/json-enc.js"></script>

<!-- The form submits JSON and targets a result div -->
<form
  id="htmx-form"
  hx-post="https://app.formkove.com/api/forms/YOUR_FORM_ID/submissions"
  hx-ext="json-enc"
  hx-target="#htmx-result"
  hx-swap="innerHTML"
>
  <div>
    <label for="htmx-name">Name</label>
    <input id="htmx-name" name="name" type="text" required>
  </div>
  <div>
    <label for="htmx-email">Email</label>
    <input id="htmx-email" name="email" type="email" required>
  </div>
  <div>
    <label for="htmx-message">Message</label>
    <textarea id="htmx-message" name="message" required></textarea>
  </div>

  <button type="submit">Send Message</button>

  <div id="htmx-result"></div>
</form>

<script>
  // Strip custom HX- headers to satisfy target CORS preflight policies
  document.body.addEventListener('htmx:configRequest', function(e) {
    for (const header in e.detail.headers) {
      if (header.toLowerCase().startsWith('hx-')) {
        delete e.detail.headers[header];
      }
    }
  });

  // Handle backend responses (success & error message parsing)
  document.body.addEventListener('htmx:afterOnLoad', function(e) {
    if (e.detail.elt.id === 'htmx-form') {
      const result = document.getElementById('htmx-result');
      try {
        const json = JSON.parse(e.detail.xhr.responseText);
        if (e.detail.xhr.status === 201) {
          result.innerHTML = '<p class="text-green-600">Message sent successfully!</p>';
          e.detail.elt.reset();
        } else {
          result.innerHTML = '<p class="text-red-600">' + (json.error || 'Error') + '</p>';
        }
      } catch {
        result.innerHTML = '<p class="text-red-600">Invalid response from server.</p>';
      }
    }
  });
</script>

Key Points

• HTMX sends standard key-value payloads by default. The json-enc extension encodes input data into application/json format.
• Adding the htmx:configRequest event listener is critical for removing the HX-Request, HX-Trigger, and other custom headers to prevent browser preflight CORS request failures.