block.js

exports.BlockHeader = class BlockHeader {
    constructor(version, previousBlockHeader, merkleRoot, time, nBits, nounce) {
        // 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; 
    }
};

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; 
    }
}