Step 1.) Upgrade to Debian 11 first
The process to go to Debian 12 is not as smooth as 11, when trying to upgrade from Debian 10. In fact, it doesn't work directly, so you'll first need to follow this guide to update to Debian 11, reboot and come back here if successful.
Step 2.) Update sources.list
Update your /etc/apt/sources.list like this:
deb http://........
Javascript window.onLoadThis can be used anywhere on an HTML page, my favorite (since body onLoad is not an option for me) is to use:
window.onLoad = functioncall();
Eg. to calculate the value of a form, you want to use the onLoad at the end of the form, as things are called in order of course........