Simple pub/sub TypeScript class

pubsub.ts

export default class PubSub {

    private topics: { [id: string] : PubSubTopic; } = {};
    
    private constructor(){ 
    }

    public static subscribe(topic:string, listener:(args:any)=>void) : void {
        this.getInstance().subscribeToTopic(topic, listener);
    }

    public static publish(topic:string, arg:any) : void {
        this.getInstance().publishToTopic(topic, arg);
    }

    private static getInstance() : PubSub {
        if(!window['PubSub_instance']) {
            window['PubSub_instance'] = new PubSub();
        }
        return window['PubSub_instance'];
    }

    private subscribeToTopic(topic:string, listener:(args:any)=>void): void {
        this.getTopic(topic).subscribe(listener);
    }

    public publishToTopic(topic:string, arg:any) : void {
        this.getTopic(topic).notify(arg);
    }

    private getTopic(name:string): PubSubTopic {
        if(!this.topics.hasOwnProperty(name)) 
            this.topics[name] = new PubSubTopic();
        
        return this.topics[name];
    }
}


class PubSubTopic {
    
    public subscriptions: ((arg:object) => void)[];

    private _lastArg:object; 

    constructor(){
        this.subscriptions = [];
        this._lastArg = null;
    }

    public subscribe(func:(arg:object) => void) {
        this.subscriptions.push(func);

        //Publish the last event for this topic to the new subscription
        if(this._lastArg) {
            func(this._lastArg);
        }
    }

    public notify(arg:object) : void {
        this._lastArg = arg;
        this.subscriptions.forEach((subscription) => {
            subscription(arg);
        });
    }
}