Observer decorator for unsubscribe on ngOnDestroy - Angular 4

subscriptions.ts

import { ISubscription } from 'rxjs/Subscription';

/**
 * Subscription holder that will call ubsubscribe() function when ngOnDestroy
 */
export function Observer() {
    return function logProperty(target: any, key: string) {

        const observerKey = 'OB' + key;
        const observerValue = 'observerSOD';
        const originalOnDestroy = target.ngOnDestroy;

        target.constructor.prototype[observerKey] = observerValue;

        target.ngOnDestroy = function () {
            originalOnDestroy();
            for (const prop in this) {
                const value: any = this[prop];
                if (value == observerValue) {
                    const subscription: ISubscription = this[prop.replace('OB', '')];
                    subscription.unsubscribe();
                }
            }
        }

    }
}