How do I extend a TypeScript class definition in a separate definition file?

Question

I have a JS library called leaflet which has an existing TypeScript definition file.

I wish to use a plugin which extends some of the objects in leaflet with an extr

Answer 1

This is what I tried and it feels relatively comfortable for me

declare module L {
    export class CircleMarkerEx {
        constructor(source: CircleMarker);
        public bindLabel(name: string, options: any): CircleMarker;
    }
    export function ex(cm: CircleMarker): CircleMarkerEx;
}

where CircleMarkerEx and ex can be defined as

class CircleMarkerExtender extends CircleMarker {    
    public b() {
        return `${this.a()} extended`;
    }
}
CircleMarker.prototype = Object.create(CircleMarkerExtender.prototype);
CircleMarker.prototype.constructor = CircleMarker;

export function ex(cm: CircleMarker) {
    return cm as CircleMarkerExtender;
}

then

let cm = ex(circle).bindLabel("name", {});

but it is still a little strange