Fire the dev, or educate the dev. Sure, eval is just a sure sign of a lot of lack of understanding, but I'd hope for something less vile as eval would be a little more understanding that everyone learns something sometime
It's gross negligence of the dev is only a Javascript dev, but maybe understandable if it's just one of the three languages he uses regularly. I probably wouldn't fire, but I also can't imagine any of my devs doing that.