Empowered angular form control

index.ts

type StatusChange = (property: string, previousValue: any, value: any) => void;
interface EmpoweredStatus {
    property: string;
    value: any;
    previousValue: any;
}

class EmpoweredFormControl<T extends AbstractControl> {
    private static readonly EMPOWER_KEY = '##empower##';
    private statusChangeHandlers: StatuChange[] = [];
    private empoweredStatusSubject = new Subject<EmpoweredStatus>();

    static getEmpoweredControl<T extends AbstractControl>(abstractControl: T): EmpoweredFormControl<T> {
        if (!abstractControl[EmpoweredFormControl.EMPOWER_KEY]) {
            abstractControl[EmpoweredFormControl.EMPOWER_KEY] = new EmpoweredFormControl(abstractControl);
        }

        return abstractControl[EmpoweredFormControl.EMPOWER_KEY];
    }

    static destroyEmpoweredControl<T extends AbstractControl>(abstractControl: T): void {
        if (abstractControl[EmpoweredFormControl.EMPOWER_KEY]) {
            delete abstractControl[EmpoweredFormControl.EMPOWER_KEY];
        }
    }

    private constructor(readonly abstractControl: T) {
        this.empowerAbstractControl(this.abstractControl);
    }

    destroy() {
        this.statusChangeHandlers = null;
        EmpoweredFormControl.destroyEmpoweredControl(this.abstractControl);
    }

    registerStatusChange(fn: StatuChange): void {
        this.statusChangeHandlers.push(fn);
    }

    get empoweredStatusChange(): Observable<EmpoweredStatus> {
        return this.empoweredStatusSubject.asObservable();
    }

    private change(property: string, previousValue: any, currentValue: any) {
        this.statusChangeHandlers.forEach(handler => {
            handler(property, previousValue, currentValue);
        });
    }

    private empowerAbstractControl(abstractControl: T) {
        ['touched', 'pristine'].forEach(property => {
            for (let baseProperty of ['_' + property, property]) {
                let propertyValue: any = abstractControl[baseProperty];
                if (propertyValue !== undefined) {
                    Object.defineProperty(abstractControl, baseProperty, {
                        get: () => propertyValue,
                        set: (value: any) => {
                            let previousValue = propertyValue;
                            propertyValue = value;
                            this.change(property, previousValue, propertyValue);
                        }
                    });
                    break;
                }
            }
        });

        this.registerStatusChange((property: string, previousValue: any, value: any) => {
            this.empoweredStatusSubject.next({
                property,
                value,
                previousValue
            });
        });
    }
}