如何从Observable<T>继承？

import { Observable, Subscriber } from 'rxjs';

class CustomObservable<T> extends Observable<T> {
  constructor(private sourceData: T[], private delayMs: number) {
    super((subscriber: Subscriber<T>) => {
      let index = 0;
      const emitNextValue = () => {
        if (index < this.sourceData.length) {
          subscriber.next(this.sourceData[index++]);
          setTimeout(emitNextValue, this.delayMs);
        } else {
          subscriber.complete();
        }
      };
      emitNextValue();
    });
  }

  // 自定义方法示例
  public transform<U>(mapper: (value: T) => U): CustomObservable<U> {
    return new CustomObservable<U>(
      this.sourceData.map(mapper),
      this.delayMs
    );
  }
}

// 使用示例
const data = [1, 2, 3];
const customObs = new CustomObservable<number>(data, 1000);

customObs.subscribe({
  next: (value) => console.log(`Received: ${value}`),
  complete: () => console.log('Completed'),
});

// 使用自定义方法
const transformed = customObs.transform(x => x * 2);
transformed.subscribe(value => console.log(`Transformed: ${value}`));