gistfile1.js

const fs = require('fs')
const path = require('path')
const csv = require('csv')
const request = require('request')

const getRemoteFileContent = (url) => {
  return new Promise((resolve, reject) => {
    request(url, (err, response) => {
      if (err) return reject(err)
      return resolve(response.body)
    })
  })
}

// parse the csv into a JSON structure -- { '01': 'KS', ... }
const transformStateFile = (csvData) => {
  return new Promise((resolve, reject) => {
    csv.parse(csvData, { delimiter: '|', from: 2 }, (err, data) => {
      if (err) return reject(err)

      return resolve(data.reduce((result, row) => {
        result[row[0]] = row[1]
        return result
      }, {}))
    })
  })
}

const transformCdZipFile = (csvData, states) => {
  return new Promise((resolve, reject) => {
    csv.parse(csvData, { from: 2 }, (err, data) => {
      if (err) return reject(err)

      return resolve(data.reduce((result, row) => {
        // Not a valid row if there aren't exactly 3 columns
        if (row.length !== 3) return result

        const cdKey = `${states[row[0]]}-${row[2]}`

        if (!result[cdKey]) result[cdKey] = []
        result[cdKey].push(row[1])

        return result
      }, {}))
    })
  })
}

const writeDataToFile = (filePath, cdZips) => {
  return new Promise((resolve, reject) => {
    fs.writeFile(filePath, JSON.stringify(cdZips), (err, result) => {
      if (err) return reject(err)
      return resolve(result)
    })
  })
}

getRemoteFileContent('https://www2.census.gov/geo/docs/reference/state.txt')
  .then(transformStateFile)
  .then(states => {
    return getRemoteFileContent('https://www2.census.gov/geo/relfiles/cdsld16/natl/natl_zccd_delim.txt')
      // First line of csvData is garbage
      .then(csvData => transformCdZipFile(csvData.split('\n').slice(1).join('\n'), states))
  })
  .then(cdZips => {
    return writeDataToFile('./data/cd-zips.json', cdZips)
  })
  .then(() => { console.log('Done!') })
  .catch(console.log)