Convert a hex string of 8 bytes into a BigInt.

littleEndian64ToBigInt.js

// Converts a hex string of 8 bytes into a BigInt.
// Useful for converting Ethereum's Beacon Deposit Contract get_deposit_count().
// https://etherscan.io/address/0x00000000219ab540356cBB839Cbe05303d7705Fa
function littleEndian64ToBigInt(bytes) {
  bytes = bytes.replace('0x', '').replaceAll(/\s/g, '');
  return new DataView(Uint8Array.from(bytes.matchAll(/.{2}/g), b => parseInt(b, 16)).buffer).getBigUint64(0, true);
}

// Example:
// littleEndian64ToBigInt('0x0519160000000000')
// 1448197n