Implementing onLoad callback for script so it should be working when js is delayed

[dewolkenwagen]

From WP org:
I use lscache to optimize website and it has option to delay JS until first interaction. Boxzilla won’t work anymore unless it’s excluded. It would be good to include it in delay however, can you try implementing onLoad callback for script so it should be working when js is delayed?

https://wordpress.org/support/topic/improving-page-load/