exploring HD key derivation

hdkeys.js

/*
BIP32 - Hierarchical Deterministic Wallet defines the semantics of a derivation path

This is some examples for paths mapped to Ethereum addresses

0               invalid (must start with m)
m               0x9b4aeeec68a20e186e98a404312869ff3330eac3
m'              0x9b4aeeec68a20e186e98a404312869ff3330eac3 (there's only 1 master)
m/              invalid
m/0             0x80e76859d6615e17c3fef155903fa9062c7bacc7 - this is the default account (child 0)
m/0'            0xd93fb97bf78b67abb415d4e56fa040efbb6662da
m/44'/60'/0'/0  0xcdda29172785891bc5ab854817457ef51c74d7c5 (Ethereum default)
m/1337/0        0xa4033517055034e69e6f8981eb44cd1a026037ea


BIP43 - Purpose Field for Deterministic Wallets
Specified that the first level of the BIP32 tree structure shall denote the "purpose". m/0' is alread "taken" (default account)

BIP44 - Multi-Account Hierarchy for Deterministic Wallets
Specified that paths with purpose 44' (hardened) shall have paths according the BIP44 schema: m/44'/coin_type'/account'/change/address_index
This makes sense for UTXO, not so much for account based systems. Adopted anyway.
Ethereum default: m/44'/60'/0'/0
*/

// inspiration source: https://github.com/kennethhutw/BIP32/blob/master/index.js

W = require('ethereumjs-wallet');
bip39 = require('bip39');

HDKey = W.hdkey;
mnemonic = 'violin exact grit step ask enforce stock floor rival man trim actress';
bip39.mnemonicToSeed(mnemonic).then(s => {
        seed = s;
        nodeM = HDKey.fromMasterSeed(seed);
        privExtKey = nodeM.privateExtendedKey();
        console.log(`private extended key: ${privExtKey}`);
        pubExtKey = nodeM.publicExtendedKey();
        console.log(`public extended key: ${pubExtKey}`);

        // every node is of type HDKey, has a method getWallet()
        // deriveChild(0) is equivalent to derivePath("m/0")
        console.log("nodeM.deriveChild(0):       ", nodeM.deriveChild(0).getWallet().getAddressString());
        console.log('nodeM.derivePath:("m/0")    ', nodeM.derivePath("m/0").getWallet().getAddressString());

        console.log("nodeM.derivePath(m/1337/0): ", nodeM.derivePath("m/1337/0").getWallet().getAddressString());

        node1337 = nodeM.derivePath("m/1337");

        console.log("node1337.deriveChild(0):    ", node1337.deriveChild(0).getWallet().getAddressString());
});

// output:
/*
$ cat ~/bin/node-init-with 
node -i --experimental-repl-await -e "`cat $1`"

$ node-init-with hdkeys.js 
Welcome to Node.js v14.18.3.
Type ".help" for more information.
> private extended key: xprv9s21ZrQH143K25crXSo1GZmL4MXHJCyg8KRdJQyHPYLMwQYGQ7Gj8hTRokQLao8xTsNzC9Da4qnv4Fh4G19Jm2eQqBH8aAaF3
public extended key: xpub661MyMwAqRbcEZhKdUL1dhi4cPMmhfhXVYME6oNtwssLpCsQweaygVmuf1LtgjBENLf5LBD1MLx9UUsFDStmWtBF3maoS1wfC
nodeM.deriveChild(0):        0x80e76859d6615e17c3fef155903fa9062c7bacc7
nodeM.derivePath:("m/0")     0x80e76859d6615e17c3fef155903fa9062c7bacc7
nodeM.derivePath(m/1337/0):  0xa6b11544f9a540c1b320f06526d2742489b394c9
node1337.deriveChild(0):     0xa6b11544f9a540c1b320f06526d2742489b394c9
*/