I see the following code in https://github.com/Microsoft/TypeScriptSamples/blob/master/t... , For me, it is definitively not the JS I know.

  declare var _: {

    each<T, U>(arr: T[], f: (elem: T) => U): U[];

    delay(f: Function, wait: number, ...arguments: any[]): number;

    template(template: string): (model: any) => string;

    bindAll(object: any, ...methodNames: string[]): void;

  };

  declare var Store: any;

If there is bug in this code, I won't know how to debug it.

I have no clue on what the JS generated by it looks like.

If I have to ask some JS programmer with no TS experience to integrate this "ts library" into their app and make sure the integrated app works on all browsers. I would have no clue on the complexity of the task just as I have no clue on how complex it was to make the GWT generated JS app to work on all browsers.

If it is just a JQuery / JS app, I can have 80-90% confident on schedule and quality of the app delivery.

But that's me, like I said, I am too old... :-)