https://github.com/LedgerHQ/ledgerjs/issues/156

ledgerjs-tetch-xpubkey-from-apps.js

import { map, compose, dropLast, last, length } from 'ramda'
import { crypto, HDNode } from 'bitcoinjs-lib'
import * as BIP32 from 'bip32'
import BIP39 from 'bip39'
import Transport from "@ledgerhq/hw-transport-node-hid"
import AppBtc from "@ledgerhq/hw-app-btc"
import * as bippath from 'bip32-path'

const mnemonic = 'deer scout bonus forward rubber rate embrace street tragic know wife tongue photo stool rival century cruise inspire cinnamon before sudden include strong flip'

export const compressPublicKey = publicKey => {
  let prefix = (publicKey[64] & 1) !== 0 ? 0x03 : 0x02
  let prefixBuffer = Buffer.alloc(1)
  prefixBuffer[0] = prefix
  return Buffer.concat([prefixBuffer, publicKey.slice(1, 1 + 32)])
}

export const fingerprint = publickey => {
  let pkh = compose(crypto.ripemd160, crypto.sha256)(publickey)
  return ((pkh[0] << 24) | (pkh[1] << 16) | (pkh[2] << 8) | pkh[3]) >>> 0
}

const getParentPath =
  compose(
    array => bippath.fromPathArray(array).toString(),
    dropLast(1),
    path => bippath.fromString(path).toPathArray()
  )

const createXPUB = (path, child, parent) => {
  let pathArray = bippath.fromString(path).toPathArray()
  let pkChild = compressPublicKey(Buffer.from(child.publicKey, 'hex'))
  let pkParent = compressPublicKey(Buffer.from(parent.publicKey, 'hex'))
  let hdnode = BIP32.fromPublicKey(pkChild, Buffer.from(child.chainCode, 'hex'))
  hdnode.parentFingerprint = fingerprint(pkParent)
  hdnode.depth = pathArray.length
  hdnode.index = last(pathArray)
  return hdnode.toBase58()
}

const getXPUB = async (ledger, path) => {
  let parentPath = getParentPath(path)
  let child = await ledger.getWalletPublicKey(path)
  let parent = await ledger.getWalletPublicKey(parentPath)
  return createXPUB(path, child, parent)
}

////////////////////////////////////////////////////////////////////////////////
const testXPUB = (mnemonic, i) => {
  // assume bitcoin mainnet for the exercise
  let seed = BIP39.mnemonicToSeed(mnemonic)
  let masterNode = HDNode.fromSeedBuffer(seed)
  return masterNode.deriveHardened(44)
                                  .deriveHardened(0)
                                  .deriveHardened(i)
                                  .neutered()
                                  .toBase58()
  }

const connect = async (ledger) => {
  let transport = await Transport.create()
  let btc = new AppBtc(transport)
  return btc
}

const main = async () => {
  let ledger = await connect()
  let xpub = await getXPUB(ledger, "44'/0'/0'")
  console.log('expected XPUB: ', testXPUB(mnemonic, 0))
  console.log('created XPUB: ', xpub)
}

// IT REQUIRES YOUR LEDGER CONNECTED WITH YOUR BTC APP RUNNING
main()