How to use sum operator of rxjs?

Delfin :

Things I have tried include following where values is array of values of which I want to find the sum.

I have also added necessary functions from rxjs as follows: I get an error saying

typeError: Rx.Observable.from(...).sum is not a function

           const { merge , interval ,from} = rxjs;
           const { tap ,take ,sum } = rxjs.operators;                
           var sumSource = Rx.Observable.from(values).sum(function (x) {
                return x;
            });

            var subscription = sumSource.subscribe(
                function (x) {
                    console.log('Next: ' + x);
                    x.target.value = x;
                },
                function (err) {
                    console.log('Error: ' + err);
                },
                function () {
                    console.log('Completed');
                });

Not much is available about sum on internet.Any inputs to fix and get the sum?

Jonathan Stellwag :

sum: regarding the official rxjs github repository they do not export/provide the sum operator anymore.
reduce operator reduce applies an accumulator function over the source Observable, and returns the accumulated result when the source completes.
scan operator scan applies an accumulator function over the source Observable and returns the accumulated result every emit.

setup

const values = [1,2,3,4,5];
const accumulator = (acc, curr) => acc + curr;

implement reduce

from(values).pipe(
  reduce(accumulator, 0)
)
// Expected output: 15

implement scan

from(values).pipe(
  scan(accumulator, 0)
)
// expected output: 1, 3, 6, 10, 15

I made a running stackblitz here.

How to use sum operator of rxjs?

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