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How to track any form submission with the dataLayer

Live guide · Checked 28 October 2026 · Updated 28 October 2026 · Checked every week against dataLayer's own help pages

One small script that pushes generate_lead for every successful form on your site, including forms that send without reloading the page.

Time

20 minutes

You will need

• Google Tag Manager on your site
• The dataLayer and generate_lead trigger from the first Secret Setup

Stuck?

Troubleshooting or ask us a question

Step by step

1. Know which kind of form you have

   There are two kinds. Reload forms go to a thank-you page after sending. AJAX forms show a message on the same page. Send a test and watch the address bar: if it changes, it's a reload form.

2. Reload forms: push on the thank-you page

   Add this to the thank-you page only (or as a Tag Manager Custom HTML tag on a Page View trigger where Page Path equals your thank-you path):

   HTMLCopy

   <script>
     window.dataLayer = window.dataLayer || [];
     window.dataLayer.push({ event: 'generate_lead', form_id: 'contact-form', lead_type: 'enquiry', value: 50, currency: 'GBP', lead_id: 'L-' + Date.now() });
   </script>

   People who refresh the thank-you page would count twice, so mark it once per visit with the tip below.

3. AJAX forms: listen for the success

   Most form tools say when a send worked. If yours doesn't, this script watches for the success message appearing. Change the selector to your form's success message:

   HTMLCopy

   <script>
   (function () {
     var SUCCESS = '.form-success';            // the element that appears after a good send
     var sent = false;
     new MutationObserver(function () {
       var el = document.querySelector(SUCCESS);
       if (!sent && el && el.offsetParent !== null) {
         sent = true;
         window.dataLayer = window.dataLayer || [];
         window.dataLayer.push({ event: 'generate_lead', form_id: (el.closest('form') || {}).id || 'ajax-form', lead_type: 'enquiry', value: 50, currency: 'GBP', lead_id: 'L-' + Date.now() });
       }
     }).observe(document.body, { childList: true, subtree: true, attributes: true });
   })();
   </script>

4. Add it through Tag Manager

   In Tag Manager: Tags > New > Custom HTML. Paste the script, tick Support document.write off (leave it off), and set the trigger to All Pages (or only the pages with the form). Save.

5. Stop double counts on refresh

   For thank-you pages, wrap the push so it only runs once per visit:

   JavaScriptCopy

   if (!sessionStorage.getItem('lead_sent')) {
     sessionStorage.setItem('lead_sent', '1');
     window.dataLayer.push({ event: 'generate_lead', form_id: 'contact-form', lead_type: 'enquiry', value: 50, currency: 'GBP', lead_id: 'L-' + Date.now() });
   }

6. Test with a real send

   Open Preview, send the form properly, and check generate_leadCopy appears once in Tag Assistant with the right form_idCopy. Send it with a mistake too: nothing should fire.

7. Publish

   Submit and Publish. Every tag already on the CE - generate_leadCopy trigger now counts this form.