MarkerCluster LeafletJS plugin TypeScript definition file creation

There are a lot of different conventions for creating "classes" in JavaScript, and TypeScript doesn't know anything about any of them. What you have in leaflet.markercluster.ts is legal JavaScript and therefore legal TypeScript, but it's not broken into classes as TypeScript understands them and that's why the declaration file generated for it is empty.

Except in rare cases declaration files are created by hand, and that's probably what you're going to have to do here. It will probably start off something like this:

/// <reference path="leaflet.d.ts" />
declare module L {
    export class MarkerClusterGroup extends FeatureGroup {
        initialize(options: any): void;
        addLayer(layer:ILayer):MarkerClusterGroup;
        addLayer(layer:LayerGroup):MarkerClusterGroup;
        // and so on and so forth
    }
}

I've had to create a couple declaration files myself and after a short learning curve it's not too hard. I found this blog post to be super helpful for getting started (props to Steve if you're reading this) and then learning by example on definitelytyped.

Once you're happy with your declaration file remember to contribute back to definitelytyped for warm fuzzy feelings.

It looked to me like the contribution has never happened, so I just submitted a PR to DefinitelyTyped for leaflet.markercluster to get those warm and fuzzy feelings :)

Has most of the common options but obviously would love if someone added more (and wrote more tests!)

https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/leaflet.markercluster/index.d.ts

leaflet.marketcluster.ts appears to be just JavaScript code, it does not contain any TypeScript class declaration.

You should create a definition file leaflet.marketcluster.d.ts instead (and leave the original leaflet.marketcluster code as just JavaScript):

declare module L {

    export interface MarkerClusterGroupOptions {
        maxClusterRadius?: number;
        // etc.
    },

    export class MarkerClusterGroup extends FeatureGroup {
        initialize(options: MarkerClusterGroupOptions);
        addLayer(layer: LayerGroup);
        // etc.
    }

    //etc ...
}