JavaScript ES6 Class Singleton

Singleton.js

(function(){
    class A {
        static getInstance() {
            if (!this.hasOwnProperty('_instance')) {
                this._instance = new this;
				console.log(`new instance of ${this._instance}`);
            }

            return this._instance;
        }

        toString() {
            return '{A}';
        }
    }

    class B extends A {
        toString() {
            return '{B}';
        }
    }
    class C extends A {
        toString() {
            return '{C}';
        }
    }
    class D extends C {
        toString() {
            return '{D}';
        }
    }

    console.log([
        A.getInstance(),
        B.getInstance(),
        B.getInstance(),
        A.getInstance(),
        C.getInstance(),
        D.getInstance(),
    ]);
})();

/*
    new instance of {A}
    new instance of {B}
    new instance of {C}
    new instance of {D}
    [A, B, B, A, C, D]
*/