Here's what this demo does:

  1. Click on the link. It will redirect to some tracking site (possibly on a different domain.)
  2. That tracking site does an AJAX request to fetch a tracking ID.
  3. The AJAX request responds with an ETag.
  4. The tracking site uses the referer header to bounce back to this page.
  5. When bouncing back, it transfers the tracking ID. In this demo, it's included as a query param.

Here are some tracking sites. They are from different domains. You can pick one and see what tracking ID it returns.

The returned tracking ID should be consistent, even if you're calling the site from a different origin.


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