使用Ajax发送统计信息

I would like to write a function to send some collected information from my web application as statistics, what I need is

Sending information to the server without waiting for a feedback

I was told you use HEAD request to ignore the request body, then how can I send the statistics (I don't want to send them in the url)

To summarise, my question is:

1. What is the best way to send statistics?
2. How to send data in a HEAD request without including them in the URL (GET)?

Any advice is very welcome.

Additionally I cannot use any library, all I should use is pure javascript