Hello,
Since 6.0 (Sep. 2019), custom rules implemented on SonarJS (the SonarQube plugin for JS analysis) are deprecated, you should avoid using this feature.
As an alternative, we advise you to write your custom rules based on Eslint, and then import them thanks to the external issues feature (see sonar.eslint.reportPaths key).
I believe this is a nice alternative, ESlint is a powerful tool, we are using it ourselves for the majority of our rules, and you will find plenty of documentation out here in case you are stuck.
Best,
Quentin