untilDestroyed Angular Component Operator

until-destroyed.operator.ts

import { Observable, Subject } from 'rxjs';
import { takeUntil } from 'rxjs/operators';

export const untilDestroyed = <C extends any>(
  componentInstance: C,
  destroyMethodName = 'ngOnDestroy'
) => <T>(source: Observable<T>) => {
  const originalDestroy = componentInstance[destroyMethodName];
  if (typeof originalDestroy !== 'function') {
    throw new Error(
      `${
        componentInstance.constructor.name
      } is using untilDestroyed but doesn't implement ${destroyMethodName}`
    );
  }
  if (!componentInstance['__takeUntilDestroy']) {
    componentInstance['__takeUntilDestroy'] = new Subject();

    componentInstance[destroyMethodName] = function(this: C) {
      typeof originalDestroy === 'function' && originalDestroy.apply(this, arguments);
      componentInstance['__takeUntilDestroy'].next(true);
      componentInstance['__takeUntilDestroy'].complete();
    };
  }

  return source.pipe(takeUntil<T>(componentInstance['__takeUntilDestroy']));
};