checking the validity of collectionVolume in a functional way

AnyJunk-collection-functional.js

// @flow
import Maybe from 'folktale/data/maybe'
import Result from 'folktale/data/result'

const MAX_VOLUME = 100

type CollectionState = {
  volume: number,
}
function safeGetCollectionVolume(data: CollectionState): Maybe<number> {
  return Maybe.fromNullable(data)
    .chain(d => Maybe.fromNullable(d.volume))
}

function validateCollectionVolume(maybeCollectionVolume: Maybe<number>): Result<string, number> {
  return maybeCollectionVolume
    .map(volume => {
      if (volume >= MAX_VOLUME) {
        return Result.Error('Volume exceeding the maximum allowed')      
      }
      return Result.Ok(volume)
    })
    .getOrElse(Result.Error('Invalid volume'))
}

// validCollectionVolume() returns a Result that can be passed safely from one edge to the other of stack
// and used both in business logic and presentation
validateCollectionVolume(safeGetCollectionVolume(data))
  .matchWith({
    Error: ({value}) => {
      // display error
    },
    Ok: ({value}) => {
      // value is the validated volume
    },
  })