JavaScript is a toy language wherein I shake my head in disbelief every day that it is my primary language, but I have found it is possible to write typesafe co

JavaScript is a toy language wherein I shake my head in disbelief every day that it is my primary language, but I have found it is possible to write typesafe code with vanilla JavaScript. With tooling and a rigid coding style observed by all developers, I'd say medium-to-large codebases (100K and up) can be maintained and extended just as well as other C-like languages. Using ultrastrict tools like Google Closure Compiler in conjunction with JSDoc comments gives you type checking along with minification and closure elimination. If you don't want the harsh taskmaster that Closure Compiler can be, IDE's like IntelliJ are able to navigate (with plugin helpers) your Node.JS codebase and build a useful type library. Again, JSDoc comments are critical here, and if you markup your JavaScript accurately and completely, you wind up with an editor that gives you very good type correctness warnings and inspections. Just keep your eyes peeled for yellow highlights and squiggly lines, and you can have confidence that your codebase is clean. JSDoc is very verbose, which is a shame, and you have to get good at forming types that are conducive to its tags. A good coding style document can go a long way to making that possible. I've found boring JavaScript groks best for all tooling. I stay away from mixins and mostly stick to boring old JS prototype definitions where the mutable bits are @type'd and assigned in the constructor to 'this'. Chrome can JIT these types of prototypes the best. Of course, there's no substitute when maintaining a large code base than to run with a comprehensive test suite.