You can include the cdn version of dayjs in a ui-template node as well. (or serve it up via http-in/out to have it available 'locally')
There is a basic walk-through in the documentation
Side note, did you ever consider putting the documentation through AI to make it simple and to the point, ELI5 ? People don't have/take time to read pages and pages full of notes, tips, pitfalls of css, javascript, ecma standards etc. (ie. how relevant is it), it makes it all very confusing.
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