What am I doing wrong when calculating the BitCoin Base58 Private Key?

Question

I have this:

const crypto = require('crypto')
const bs58 = require('bs58')

const a = crypto.randomBytes(32)
const b = crypto.createHash('sha256').update(a).digest('hex')
const c = '80' + b
const d = crypto.createHash('sha256').update(c).digest('hex')
const e = crypto.createHash('sha256').update(d).digest('hex')
const f = c + e.substr(0, 4)
const bytes = Buffer.from(f, 'hex')
const address = bs58.encode(bytes)
console.log(address)

Which was inspired from this. But when I do this:

 bitcoin-cli importprivkey "<key>" "foo"

I get this:

error code: -5
error message:
Invalid private key encoding

What am I doing wrong?