Rxjs operators: scan vs. reduce
Thursday, October 29, 2020
Rxjs operators: scan vs. reduce
The scan and reduce RxJS operators are two very similar operators that work very much like the reduce() method of arrays.
The difference is an observable created with scan will emit on each source emission, whereas reduce will emit only once on completion.
Code Examples
scan-vs-reduce
const source$ = interval(1000).pipe(take(4));
// source$: -0-1-2-(3|)
const usingScan$ = source$.pipe(scan(
(acc, curr) => acc + curr,
0
));
// usingScan$: -0-1-3-(6|)
const usingReduce$ = source$.pipe(reduce(
(acc, curr) => acc + curr,
0
));
// usingReduce$: -------(6|)
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