I use pycharm with typescript, and either I have a new version or the pycharm plugin is far different to the webstorm one. All the refactoring options, jump-to-symbol, type hinting, type completion and inline-error checking work really well for me.

There are some pain points to be sure (modules, generics that don't quite work), but:

- Emits known good javascript patterns, preventing javascript's typical '50 ways of doing something'.

- Interacts cleanly and nicely with the existing javascript ecosystem.

- The emitted javascript runs on old browsers, and is only marginally bigger than the source code, smaller sometimes, if you use interfaces

- Clean module system (a little irritating to use perhaps, but still) supporting AMD and CommonJS (this is absolutely the future for JS dependencies).

- Open source, installable compiler using npm.

What's the alternative?

    - native JS      <-- Not a bad choice, needs discipline to maintain code quality
    - coffee script  <-- Interacts poorly with existing js ecosystem
    - dart           <-- Doesn't run on old browsers, poor interop
    - emscripten     <-- Massive output, poor interop

I cant say I'm any hurry to add C# into the mix, but typescript has impressed me thus far, despite being from Microsoft.