There’s ES5, ES6, then ES7, TypeScript, AtScript, Dart, Babel…the list goes on.
However, committee-driven design is notoriously slow, so everyone from independent developers to browser vendors are eager to use and implement new JS features faster than the standards organization can approve them.
Dart is an experimental language created several years ago by Google. We do not recommend using Dart as new JS features supersede it.
AtScript was an experimental language created by Google to extend JS and Typescript with new features such as annotations and type introspection. It is now defunct.
Typescript is Microsoft’s extension of JS that comes with powerful type checking abilities and object oriented features. Both Angular 2 and Ionic 2 use TypeScript.
If you’re interested in type checking and new OO features, or want to contribute to Angular 2, check out TypeScript.