functional_filter.js

let generateResponse = (data) => {
  return Promise.coroutine(function* () {

    let emails = data
                     .map(getEmailsFromIndividual)
                    .reduce(flatten)
                    .filter(value => value != undefined && value != "")
                    .filter(distinct)

    return emails
  })()
}

let getEmailsFromIndividual = (individual) => {
    if (!Array.isArray(individual.contacts)) return []
    return individual
            .contacts
            .map(value => value['emailAddress'])
}

let flatten = (flatArray, arrayElement) => {
  return flatArray.concat(arrayElement)
}

let distinct = (val, index, contacts) => {
  return contacts.indexOf(val) === index
}