Handling shared properties in TypeScript - data-structures

Question

I have a class system as shown below. And I would like to get the shared properties out/optimized toward a more maintainability data-structure.
My first thought was using an interface, but they can't contain properties in TypeScript (as far as I know). - So do you have any idea to how I can make this better?
class Particle {
position: Vector;
}
class Block extends Particle {
height: number;
width: number;
get Left(): number {
return this.position.getX();
}
get Right(): number {
return this.position.getX() + this.width;
}
}
class Sphere extends Particle{
radius: number;
get Left(): number {
return this.position.getX() - this.radius;
}
get Right(): number {
return this.position.getX() + this.radius;
}
}

Answer 1

In TypeScript you can use classes as interface definitions. You can introduce a class LeftRight that has the properties Left and Right and use this as the class definition:
class Block extends Particle implements LeftRight {
/* .... */
}
A fully working example can look like this:
class Vector {
getX (): number { return 0; }
}
class Particle {
position: Vector = new Vector();
}
class LeftRight {
get Left(): number {
throw 'Member Left not overriden';
}
get Right(): number {
throw 'Member Right not overriden';
}
}
class Block extends Particle implements LeftRight {
height: number;
width: number;
get Left(): number {
return this.position.getX();
}
get Right(): number {
return this.position.getX() + this.width;
}
}
class Sphere extends Particle implements LeftRight {
radius: number;
get Left(): number {
return this.position.getX() - this.radius;
}
get Right(): number {
return this.position.getX() + this.radius;
}
}
var block = new Block();
block.height = 100;
block.width = 100;
// note that you can safely cast to type LeftRight
var lr: LeftRight = block;
alert('Left: ' + lr.Left + ' Right: ' + lr.Right);
This is also shown in the TypeScript handbook in the Mixin example: http://www.typescriptlang.org/Handbook#mixins