TypeScript - Singleton

Singleton.ts

class Singleton {
    private static _instance:Singleton = null;
    constructor() {
        if(Singleton._instance){
            throw new Error("must use the getInstance.");
        }
        Singleton._instance = this;
    }
    public static getInstance():Singleton {
        if(Singleton._instance === null) {
            Singleton._instance = new Singleton();
        }
        return Singleton._instance;
    }
}

var singleton=Singleton.getInstance();