Long running projects in JavaScript may not be that long really. If you leave any codebase for a couple years, things would have changed so drastically, new devs may not even recognize the code. An year old JS project may be using React, a 2-year-old project could be using Angular, a 4-year old project might be using Backbone, a 6-year-old could have $("#el").bind() all over while 8 year-old project could have been in Prototype.js.