Minimum blockchain implements: referred https://github.com/lhartikk/naivechain/blob/master/main.js

blockchain.js

/* @flow */
import SHA256 from 'crypto-js/sha256'

type Block = {
  index: number,
  previousHash: string,
  timestamp: number,
  data: string,
  hash: string
}

type BlockChain = Block[]

/* initial block chain */
export function getGenesisBlock(): Block {
  return createBlock(
    0,
    '0',
    1465154705,
    'my genesis block!!',
    '816534932c2b7154836da6afc367695e6337db8a921823784c14378abed4f7d7'
  )
}

export function getLatestBlock(blockchain: BlockChain): Block {
  return blockchain[blockchain.length - 1]
}

/* implementation */

export function createBlock(
  index: number,
  previousHash: string,
  timestamp: number,
  data: any,
  hash: string
): Block {
  return {
    index,
    previousHash,
    timestamp,
    data,
    hash
  }
}

export function calculateHashForBlock(block: Block) {
  return calculateHash(
    block.index,
    block.previousHash,
    block.timestamp,
    block.data
  )
}

export function calculateHash(
  index: number,
  previousHash: string,
  timestamp: number,
  data: string = ''
): string {
  return SHA256(index + previousHash + timestamp + data).toString()
}

export function generateNextBlock(
  blockchain: BlockChain,
  blockData: string = ''
): Block {
  const previousBlock = getLatestBlock(blockchain)
  const nextIndex = previousBlock.index + 1
  const nextTimestamp = ~~(Date.now() / 1000)
  const nextHash = calculateHash(
    nextIndex,
    previousBlock.hash,
    nextTimestamp,
    blockData
  )
  return {
    index: nextIndex,
    previousHash: previousBlock.hash,
    timestamp: nextTimestamp,
    data: blockData,
    hash: nextHash
  }
}

export function isValidNewBlock(
  newBlock: Block,
  previousBlock: Block
): boolean {
  if (previousBlock.index + 1 !== newBlock.index) {
    console.log('invalid index')
    return false
  } else if (previousBlock.hash !== newBlock.previousHash) {
    console.log('invalid previoushash')
    return false
  } else if (calculateHashForBlock(newBlock) !== newBlock.hash) {
    console.log(
      'invalid hash: ' + calculateHashForBlock(newBlock) + ' ' + newBlock.hash
    )
    return false
  }
  return true
}

export function isValidChain(blockchainToValidate: BlockChain): boolean {
  // check genesis block
  if (
    JSON.stringify(blockchainToValidate[0]) !==
    JSON.stringify(getGenesisBlock())
  ) {
    return false
  }

  const tempBlocks = [blockchainToValidate[0]]
  for (var i = 1; i < blockchainToValidate.length; i++) {
    if (isValidNewBlock(blockchainToValidate[i], tempBlocks[i - 1])) {
      tempBlocks.push(blockchainToValidate[i])
    } else {
      return false
    }
  }
  return true
}

export function addBlock(blockchain: BlockChain, newBlock: Block): BlockChain {
  if (isValidNewBlock(newBlock, getLatestBlock(blockchain))) {
    return blockchain.concat([newBlock])
  }
  return blockchain
}

log.txt

miner1 checks receivedBlockchain. Size: 1
miner1 add new block: 642ea53597d4d90eca7cbc9bcdd80217b76d89dae027fb70c9b881b56e9e7710
miner1 add new block: 7eebe4fd8ef821553a8a62d5e85bce6515e954f8420401b6733dafea4c9f0673
miner1 bloadcasted
miner3 checks receivedBlockchain. Size: 3
miner3 accepted received blockchain
miner3 bloadcasted
miner1 checks receivedBlockchain. Size: 3
miner1 add new block: 03cabfbaafaa9a381118cc665f505deb157ef4d49d2969f13749a6a0771e6587
miner1 add new block: f8f903b8954dd8009bc276019b6cc446b31e87cae637f6ec2e99c7c99a496d9b
miner1 bloadcasted
miner2 checks receivedBlockchain. Size: 5
miner2 accepted received blockchain
miner2 add new block: 1feac1e2d90e1252cc1bbb3bf6ec7cab4da25787cf64d03cf600d4c534309168
miner2 add new block: c59e8fa1882dcb30b0ab43c55f0121460abc655883566789b510f59d8165d4b0
miner2 bloadcasted
miner2 checks receivedBlockchain. Size: 7
miner2 bloadcasted
miner3 checks receivedBlockchain. Size: 7
miner3 accepted received blockchain
miner3 add new block: 6e4709bac242febc16827b6d2cf3f515295b74a61439640187418d68071435bf
miner3 add new block: 42ff0c9d57434a7fa444e886f8c3bb5db1bdd2216fb87a83bc141834f4533610
miner3 bloadcasted
miner3 checks receivedBlockchain. Size: 9
miner3 bloadcasted
miner1 checks receivedBlockchain. Size: 9
miner1 accepted received blockchain
miner1 add new block: 0d1200472bf18a419a41fde1ecbb3715177e1e67f7152618840d84c2b6f91b61
miner1 add new block: 4a88da04e21bd5aafa7e874fb048e1ffd28d32059b8e3dd2ee2c628ea19da266
miner1 bloadcasted
miner3 checks receivedBlockchain. Size: 11
miner3 accepted received blockchain
miner3 add new block: 4a82941ec34034446e11b0c0cbd618a420b4416d7e4a41625888a1005ec3a8b0
miner3 add new block: 6f41d94dd78e7296bb396cd8f7193c9232c44bbf7f556ea9c23c588846ebc4ed
miner3 bloadcasted
miner2 checks receivedBlockchain. Size: 13

run.js

/* @flow */
import {
  getGenesisBlock,
  generateNextBlock,
  getLatestBlock,
  addBlock,
  isValidChain,
  isValidNewBlock
} from './blockchain'
import range from 'lodash.range'

const blockchain = [getGenesisBlock()]

// basic use
const prev = getLatestBlock(blockchain)
const next1 = generateNextBlock(blockchain, 'foo')
const newBlockchain1 = addBlock(blockchain, next1)

const next2 = generateNextBlock(newBlockchain1, 'bar')
const newBlockchai2 = addBlock(newBlockchain1, next2)

console.log('current', newBlockchai2)
console.log('isValidChain', isValidChain(newBlockchai2))

const wait = n => new Promise(resolve => setTimeout(resolve, n))

// It should not be singleton but easy to test.
let receivedBlockchain = [getGenesisBlock()]
const bloadcast = (name, next) => {
  console.log(`${name} bloadcasted`)
  receivedBlockchain = next
}

const createMiner = (name: string) => {
  let myBlockchain = blockchain.slice()

  const accept = () => {
    console.log(
      `${name} checks receivedBlockchain. Size: ${receivedBlockchain.length}`
    )
    // console.log(receivedBlockchain.length, myBlockchain.length)
    if (receivedBlockchain.length > myBlockchain.length) {
      if (isValidChain(receivedBlockchain)) {
        console.log(`${name} accepted received blockchain`)
        myBlockchain = receivedBlockchain
      } else {
        console.log('Received blockchain invalid')
      }
    }
  }

  const addNewBlock = () => {
    const next = generateNextBlock(myBlockchain)
    myBlockchain = addBlock(myBlockchain, next)
    console.log(`${name} add new block: ${next.hash}`)
  }

  return async () => {
    while (true) {
      await wait(Math.random() * 3000)
      accept()
      range(~~(Math.random() * 3)).forEach(_ => addNewBlock())
      bloadcast(name, myBlockchain)
    }
  }
}

// competitive miners
createMiner('miner1')()
createMiner('miner2')()
createMiner('miner3')()