Using Array.prototype.map

00-before.js

const URI = require('uri-js')

const uri = 'custom://recovery?token=IamToken&nextVar=nextVar'
const doTheSideEffect = (token) => console.log(token)

doTheWholeEnchilada (uri) {
  if (!uri) return
  const parsedUri = URI.parse(uri)
  const query = parsedUri.query
  const splitArray = query.split('token=')
  const nextString = splitArray[1]
  const finalArray = nextString.split('&')
  const final = finalArray[0]
  doTheSideEffect(final)
}

doTheWholeEnchilada(uri)

// what happens if uri = 'custom://recovery?nextVar=nextVar'

01-after.js

const URI = require('uri-js')
const {compose, curry, identity, isNil, not, nth, prop} = require('ramda')

const uri = 'custom://recovery?token=IamToken&nextVar=nextVar'
const doTheSideEffect = (token) => { console.log(token); return token }

const exists = compose(not, isNil)
const parse = URI.parse
const getQuery = prop('query')
const match = curry((regex, source) => source.match(regex))
const token = /token=(\w{8})/
const getMatch = match(token)
const getToken = nth(1)

const doThePureThing = (uri) => {
  return [uri]
    .filter(exists)
    .map(parse)
    .map(getQuery)
    .filter(exists)
    .map(getMatch)
    .filter(exists)
    .map(getToken)
}

doThePureThing(uri).map(doTheSideEffect)