RxJS Typescript: Property 'reduce' does not exist on type 'Observable<number>'

Question

I have this little snippet

const observable:Observable<number> = Observable.from([1, 2, 3])
  .reduce((sum: number, number: number) => {
    return sum + number
}, 0)
observable.subscribeOnNext((sum) => console.log(sum))

It works as expected, but the Typescript compiler produces this error:

error TS2339: Property 'reduce' does not exist on type 'Observable'.

If reduce is changed to scan, the error goes away (= the definition of scan is found by the compiler, but the definition of reduce not).

I'm using npm, and have typescript (2.0.10), rx (4.1.0) and @types/rx (2.5.34) installed.

It looks like a recent commit added typings, so you might be able to use that - try npm install --save Reactive-Extensions/RxJS (and remove the old version of RxJS and the types you have installed). — Aurora0001
– Aurora0001, Commented Dec 3, 2016 at 16:13
Yes, thats working, thanks! Do you want to post that as an actual answer, so I can accept? — MeXx
– MeXx, Commented Dec 3, 2016 at 17:26

Aurora0001 · Accepted Answer · 2016-12-03 17:45:13Z

1

The latest version of RxJS 4 on GitHub has added a typings declaration and the relevant d.ts files that define the types for TypeScript.

Simply upgrade to the latest version by removing the old rx and @types/rx modules and run:

npm install --save Reactive-Extensions/RxJS

Note the syntax Reactive-Extensions/RxJS which is shorthand for using the GitHub repository's source code.

answered Dec 3, 2016 at 17:45

Aurora0001

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Comments

mathi · Accepted Answer · 2018-04-28 15:30:40Z

1

Another thing that generates this error is how you import Observable. I had

import {Observable} from 'rxjs/Observable'

which caused the same error, by changing it to

import {Observable} from 'rxjs/Rx'

it resolved the reduce method correctly. Something else to check.

edited Apr 28, 2018 at 15:30

mathi

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answered Mar 29, 2018 at 16:37

Brian Bauman

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