Indeed, I've worked on billing system that relied heavily on pure JavaScript. Not even modern flavors with map/reduce, etc. - ECMAScript 5. It worked surprising

Indeed, I've worked on billing system that relied heavily on pure JavaScript. Not even modern flavors with map/reduce, etc. - ECMAScript 5. It worked surprisingly well and our bottleneck wasn't the runtime but rather the databases we were constantly upserting to. It sounds kinda crazy but with good change control, documentation, good relationship with the ETL team - it was pretty maintainable.