bitcoin-mine-block.js

const createBlock = async (publicKey : string, transactions : Array<string>) : Promise<?string> => {
    const headBlock = root.getLongestBranchNode().getValue();

    const newTransactions = await asyncFilter(transactions, verifyPackedSignature);

    const newDifficulty = (headBlock.elapsed) > BLOCK_TIME
        ? headBlock.difficulty - 1
        : headBlock.difficulty + 1;

    const newReward = divisibleBy(headBlock.index, REWARD_HALVING_SCHEDULE)
        ? Math.floor(headBlock.reward / 2)
        : headBlock.reward;

    const newBlock = {
        miner:        publicKey,
        parentid:     headBlock.id,
        index:        headBlock.index + 1,
        id:           uniqueID(),
        time:         now(),
        elapsed:      now() - headBlock.time,
        transactions: newTransactions,
        difficulty:   newDifficulty,
        reward:       newReward
    };

    const hashedBlock = await hashAndPack(newBlock);
    const hash = unpackHash(hashedBlock);

    if (divisibleBy(hash, headBlock.difficulty)) {
        return hashedBlock;
    }
};