Trackers are client or server-side libraries which track user behavior by sending events.
There are two methods of tracking:
Access to XMLHttpRequest at 'https://api.xxxx' from origin 'https://xxx'
has been blocked by CORS policy:
Response to preflight request doesn't pass access control check:
No 'Access-Control-Allow-Origin' header is present on the requested resource.
The script in a web page should be run in async mode to run early
Many browsers stop executing JavaScript as soon as the page starts unloading, therefore measuring outbound links and forms is difficult.
One solution to this problem is to use: