selectAndSubscribe-decorator for ng2-redux

selectAndSubscribe.ts

import { NgRedux } from 'ng2-redux';
import { ISubscription } from 'rxjs/Subscription';

export const selectAndSubscribe = <T>(
    statePathOrFunc?: string |
        (string | number)[] |
        Function,
    comparer?: (x: any, y: any) => boolean) => (target, key) => {

    let bindingKey = statePathOrFunc;
    if (!statePathOrFunc) {
        bindingKey = (key.lastIndexOf('$') === key.length - 1) ?
            key.substring(0, key.length - 1) :
            key;
    }

    let val: any;
    let subscription: ISubscription;

    function getter() {
      if(!subscription) {
        subscription =
          NgRedux.instance
            .select(bindingKey, comparer)
            .subscribe(newVal => val = newVal);
      }

      return val;
    }

    // Delete property.
    if (delete this[key]) {
        // Create new property with getter and setter
        Object.defineProperty(target, key, {
            get: getter,
            enumerable: true,
            configurable: true
        });
    }

    if(delete this['ngOnDestroy']) {
      let onDestroy =
        target.ngOnDestroy ? target.ngOnDestroy : () => undefined;

      let newOnDestroy = function() {
        if (subscription) {
          subscription.unsubscribe();
          subscription = undefined;
        }

        onDestroy.bind(this)();
      }

      Object.defineProperty(target, 'ngOnDestroy', {
        value: newOnDestroy
      });
    }
};