In my limited experience working with JavaScript, I've found the lack of the following to cause more problems when writing modular, reusable code than the lack of type annotations:

* a single, definitive method for creating namespaces without using a framework or library

* a single, definitive method for defining classes and using inheritance without using a framework or library

* a single, definitive method of allowing async functions to modify the state of an object without having to declare that object in the global scope, without using a framework or library

If these problems are already solved, please let me know!