I'm playing Ethernaut Level 3, so I wrote the following code to retrieve the "guess" value:

async do_guess => {
    let no     = await web3.eth.getBlockNumber()
    let block  = await web3.eth.getBlock(no)
    let factor = new web3.utils.BN('57896044618658097711785492504343953926634992332820282019728792003956564819968')
    let result = new web3.utils.BN(block.hash)

    let tmp = result.div(factor)
    return tmp.toString()
}

let value = await do_guess()
console.log(value)

But the value is always "undefined" somehow, does anyone know what's wrong?