Bitcoin Private Key to WIF

index.js

// https://en.bitcoin.it/wiki/Wallet_import_format

const crypto = require('crypto');
const base58 = require('base-58')

const sha256 = buffer => crypto.createHash('sha256').update(buffer).digest()

const privateKeyToWIF = (privateKey, prefix = 'ef', compressed = '01') => {
  const prefixedPrivateKey = prefix + privateKey + compressed
  const prefixedPrivateKeyBuffer = Buffer.from(prefixedPrivateKey, 'hex')
  const check = sha256(sha256(prefixedPrivateKeyBuffer)).slice(0, 4)
  const wifBuf = Buffer.concat([prefixedPrivateKeyBuffer, check])
  return base58.encode(wifBuf)
}

console.log(privateKeyToWIF('hex private key'))