I've worked on large production codebases in the past, for servers written in both Java (at company [a]), and JavaScript with Node.js (at company [b]).
The Java codebase was much easier to read, understand, navigate around, and debug. If a function took an argument "SomeClass foo" I could look up "SomeClass" and know exactly what it was.
In the Node codebase, if have argument "foo", you're lost with no easy way to figure out exactly what this "foo" is. You would have to run the code, set a breakpoint, and inspect "foo".
In addition, JavaScript encouraged a lot of bad coding practices that almost made me want to cry.
In the Java server, we used a JSON library where you would annotate a class, and the library would construct an object for that class. This guaranteed the JSON was well-formed, among other things.
In the Node.js codebase, people would pull something out of Mongo, chuck it in a variable "data", and then do "data.foo.bar[1].qux". (Yes, the "[1]" is real.) It was terrible.
The company that used Node.js had far less reliable code overall, and their services (written in JavaScript) would crash frequently, most commonly due to type errors.
And this is just a tip of the iceberg. There were so many problems that attributable to the choice of JavaScript as the language for a large, complex back-end system, and the failure to use any tool for type checking (like Flow), in addition to bad coding practices.
[a] Amplify Education, Inc. https://www.amplify.com/
[b] Lifion, a division of ADP. http://www.lifion.com/
