Reduce from RxJS doesn't return Object

Question

I'm working on Angular and I the reduce()operator doesn't return my object. My code is following below:

I've created an interface

interface Example {
  page?: number;
  size?: number;
  name?: string;
}

And I declared a subject to create a data stream and inside of pipe operator, I wanna create a object from the data which I sent through the this.example$.next().

exemple$ = new Subject<Example>();

  get$ = this.exemple$
    .pipe(
      startWith({}),
      reduce(
        (obj, item) => {
          Object.keys(item).forEach(data => (obj[data] = item[data]));
          console.log('obj', obj);
          return obj;
        },
        { page: 15, size: 10 } as Example
      ),
      tap(console.log)
    )
    .subscribe();

  ngOnInit() {
    this.exemple$.next({ name: 'John Paul' });
  }

When the Angular starts up, It send the data and I catch it in console.log() inside of reducer() operator and tap() operator.

I can see the data inside of reduce() but nothing happens inside of tap() . Its like as reduce is not returning the object which I'm returning inside it.

Can anyone help me? Thx

martin · Accepted Answer · 2019-09-16 22:50:10Z

1

Your source Observable is exemple$ which is a Subject. The reduce() operator will emit only after the source Observable completes which means you need to call exemple$.complete() (or have some condition that completes the chain).

Maybe you're looking for scan() instead that emits all intermediate results?

answered Sep 16, 2019 at 22:50

martin

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1 Comment

Leonardo Campadelli Over a year ago

Thx a lot, @martin. Your solution salve me!!

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