input-observable.ts

import { Input } from '@angular/core';
import { BehaviorSubject } from 'rxjs/BehaviorSubject';

export function InputObservable<T>(inputName?: string) {
    return (target: object, name: string): void => {
        const subject = new BehaviorSubject(this[name]);

        if (delete target[name]) {
            Object.defineProperty(target, name, {
                set(value: T): void {
                    subject.next(value);
                },
                get(): BehaviorSubject<T> {
                    return subject;
                },
            });
        }

        Input(inputName)(target, name);
    };
}