What to understand / diagnose from this loaded by?

I am an seo analyst. I manage my clients’ websites as well as my own websites around 5.

Lately, almost all my sites shows high first byte time. And most of the time it is by java scripts. It is like…

URL: http://website.com/
Loaded by: http://some-kind-of-java-script.js

If i remove that javascript then another java script replaces.

WHAT DOES LOADED BY MEAN?

Check example result here https://www.webpagetest.org/result/190728_ND_91d5abececd1fc42285e0fc309d77424/