This seem to have been broken. A code that would work with Windows XP Chrome 49 (also would work on 47, not on 46)...
https://pl.wikipedia.org/w/index.php?title=MediaWiki%3AGadget-sk.js&type=revision&diff=64625991&oldid=64621169

// this is broken
result.push({start, end});

// this works fine
result.push({start: start, end: end});

The problem was report by Chrome users with relatively latest version. Same code works fine when loaded as a user script.

I didn't have any linter warnings, so I guess the problem is in minification process.

There was a task for linter here: T277085. Not sure if that includes parsing JS too.