block.js

exports.BlockHeader = class BlockHeader {
  constructor(version, previousBlockHeader, merkleRoot, time, nBits, nonce) {
    // Version - at the time of writing there are 4 block versions.
    this.version = version;

    // previous block header hash - A SHA256(SHA256()) hash of previous block’s header. Ensures that previous block cannot be changed as this block needs to be changed as well.
    this.previousBlockHeader = previousBlockHeader;

    // merkle root hash - a merkle tree is a binary tree which holds all the hashed pairs of the tree.
    this.merkleRoot = merkleRoot;

    // a Unix epoch time when the miner started hashing the header.
    this.time = time;

    this.nonce = nonce; // Used in PoW
  }
};

exports.Block = class Block {
  constructor(blockHeader, index, txns) {
    this.blockHeader = blockHeader;

    // GenesisBlock is the first block - block 0
    this.index = index;

    // txns is the raw transaction in the block.
    this.txns = txns;
  }
};