reduce

signature: reduce(accumulator: function, seed: any): Observable

Reduces the values from source observable to a single value that's emitted when the source completes.

๐Ÿ’ก Just like Array.prototype.reduce()โ€‹

๐Ÿ’ก If you need the current accumulated value on each emission, try scan!

โ€‹โ€‹Ultimate RxJSโ€‹โ€‹

Examples

Example 1: Sum a stream of numbers

( StackBlitz | jsBin | jsFiddle )

// RxJS v6+
import { of } from 'rxjs';
import { reduce } from 'rxjs/operators';
โ€‹
const source = of(1, 2, 3, 4);
const example = source.pipe(reduce((acc, val) => acc + val));
//output: Sum: 10'
const subscribe = example.subscribe(val => console.log('Sum:', val));

Additional Resources

๐Ÿ“ Source Code: https://github.com/ReactiveX/rxjs/blob/master/src/internal/operators/reduce.tsโ€‹