import { assert } from 'chai' ; import { ISeries , Series } from 'data-forge' ; declare module "data-forge/build/lib/series" { interface ISeries < IndexT , ValueT > { daysFalling ( ) : ISeries < IndexT , number > ; } interface Series < IndexT , ValueT > { daysFalling ( ) : ISeries < IndexT , number > ; } } function daysFalling < IndexT = any > ( this ) { return this . direction ( 2 ) . counter ( value => value < 0 ) ; } Series . prototype . daysFalling = daysFalling ;