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  • Reduces the values from source observable to a single value that's emitted when the source completes.
  • Examples
  • Additional Resources
  1. Learn RxJS
  2. Operators
  3. Transformation

reduce

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Last updated 1 year ago

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

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

💡 Just like

💡 If you need the current accumulated value on each emission, try !

Examples

Example 1: Sum a stream of numbers

( | | )

// RxJS v6+
import { of } from 'rxjs';
import { reduce } from 'rxjs/operators';

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


📰 - Official docs

🎥 - Academind

🎥 - Kwinten Pisman

📁 Source Code:

reduce
Scan() vs reduce() | RxJS TUTORIAL
Build your own reduce operator
https://github.com/ReactiveX/rxjs/blob/master/src/internal/operators/reduce.ts
Array.prototype.reduce()
scan
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jsBin
jsFiddle