옵저버블 테스트

function observerFn(observer:Observer<number>) {
      
      const seq = [1,2,3,4];
      let timeoutId:any;

      function doSequence(arr:number[], idx:number) {       
        timeoutId = setTimeout(() => {
          observer.next(arr[idx]);
          if(idx==arr.length-1){
            observer.complete();
          }else{
            doSequence(arr, ++idx);  
          }          
        }, 1000);
      }

      doSequence(seq,0);
      
      return ()=>{ clearInterval(timeoutId) };
    }

    const sequence = new Observable(observerFn);

    sequence.subscribe({
      next(value) {
        console.log(value);
      },
      complete() {
        console.log('completed');
      },
    });