Testing extending Leaflet components via TypeScript's inheritance model

CustomLeafletMarkers.ts

/// <reference path='../leaflet/leaflet.d.ts' />
namespace L {

    type LatLngExpression = L.LatLng | number[] | ({ lat: number; lng: number });

    export var JSMarker = L.Marker.extend({

        options: { title: 'MyMarker' },

        initialize: function(latLng: LatLngExpression, options?: L.MarkerOptions) {
            L.Util.setOptions(this, options)
            L.Marker.prototype.initialize.call(this, latLng, this.options);
        },

        greet: function() {
            this.bindPopup("Hello! JS here!")
            return this;
        }
    })

    export class TSMarker extends L.Marker {
        options: L.MarkerOptions

        constructor(latLng: LatLngExpression, options?: L.MarkerOptions) {
            super(latLng, options)
        }

        greet(): this {
            this.bindPopup("Hello! TSX here!")
            return this
        }

    }
    // Default options
    TSMarker.prototype.options = {
        title: 'MyMarker',
        clickable: true,
        icon: L.icon({
            iconUrl: 'leaf-green.png',
            shadowUrl: 'leaf-shadow.png',
            iconSize: [38, 95],
            shadowSize: [50, 64],
            iconAnchor: [22, 94],
            shadowAnchor: [4, 62],
            popupAnchor: [-3, -76],
        })
    }

}

Did it works?
I am rewriting a javascript code where L.Map was extend using .extend({...}) to a typescript using class declaration and I am having stranges sides effetes.
I don't sure if .extend and typescript class declaration are equivalents or not.

@s-nt-s IIRC they're not 100% equivalent, extend does some extra things that the above code does not do, and would require additional code