Custom JavaScript
Custom JavaScript (called Userscript in Scrapbox) is more limited than custom CSS:
It has to be allowed in user settings, see /help/Userscript
It has to be put under your profile page (i.e. not under Settings)
This means, you cannot use custom JavaScript for public pages.
Links to some websites with custom JavaScript for Scrapbox.io
https://qiita.com/progfay/items/5a81e130fc36291990d4#文字をalignする #japanese
e.g. ordered outline
/scrasobox/テンプレートを使ってページを作成（UserScript版） #japanese
templates
/Mijinko/ScrapBubble #japanese
ScrapBubble example