Suggestion: Extension methods

Compiling to:

``` javascript
// js
var _Shape = {
    getArea:function() { return /* ... */; }
}
console.log(_Shape.getArea.call(x));
```

I think due to first-class functions in JS there is a problem with this approach:

``` typescript
extension class Shape { // Syntax??
    getArea() { return /* ... */; }
}
var x = new Shape();
var y = new Shape();
console.log(x.getArea); // Function or undefined?
x.getArea.foo = "bar";
console.log(y.getArea.foo); // "bar" or undefined?
```

If extension methods are to be implemented, there would probably have to be restirictions on accessing/changing their properties.

_Considering "class" syntax_

``` typescript
extension class Shape { // Syntax??
    getArea() { return /* ... */; }
}