When typing code snippet

 %%linebreak <none>
 X: 1
 K: C treble
 % C major, four octaves:
 C, D, E, F, G, A, B, C | C D E F G A B c |
 c d e f g a b c' | c' e' g' c'' |
in Making Music with Abc 2 - A practical guide to the Abc notation, it was expected to show the staff in one line, however it showed like this:

I once thought the editor width was not enough, actually it was wide enough to display:

Then I found this issue and "the plugin is currently using the latest (officially released, non-beta) version of abcjs" caught my eyes.

So I searched for ABC standard 2.2, and found that I:<directive> took place of %%<directive>:

So, I modified it to

 I: linebreak <none>
 X: 1
 K: C treble
 % C major, four octaves:
 C, D, E, F, G, A, B, C | C D E F G A B c |
 c d e f g a b c' | c' e' g' c'' |
However it still didn't work:

Either I:<directive> or %%<directive> worked well in EasyABC, but neither of them worked in ABCJS Editor. Is this caused by the changes of the ABC standard?

 The answer is yes.

 X: 1
 K: C treble
 % C major, four octaves:
 C, D, E, F, G, A, B, C | C D E F G A B c |\
 c d e f g a b c' | c' e' g' c'' |

So we just need a backslash, and it do work.
With Win11 23H2, Obsidian 1.6.7 and ABC Music Notation plugin Version 1.4.0, left at Sept 26, 2024.