An example blockchain implementation in Node.js to understand the concept behind

blockchain.js

// example usage

const blockchain = new Blockchain();
blockchain.add(1);
blockchain.add(2);
blockchain.add(3);
blockchain.verify();
console.log(blockchain);

// example output

/* 
$ node blockchain.js 
Blockchain {
  blocks: 
   [ { timestamp: 2018-01-24T10:02:07.395Z,
       data: 1,
       hash: 'b9b92d5db0fbe77b2600ecc5bc36b7938d7185bbdb5b39e399374209e16e877e' },
     { timestamp: 2018-01-24T10:02:07.395Z,
       data: 2,
       hash: '569d2ccfd87b7a7b0203e2d160cd4fffc05a831c89a5f5d626cfa245e887a197' },
     { timestamp: 2018-01-24T10:02:07.395Z,
       data: 3,
       hash: 'adb97d934aafe7bd0cc943c2920f512baaed44e37bef5dad3177d8f798200db7' } ],
  secret: '' }
 */

// example implementation

const crypto = require('crypto');

class Blockchain {
  constructor(secret = '') {
    this.blocks = [];
    this.secret = secret;
  }

  hash(data) {
    return crypto.createHash('sha256').update(JSON.stringify(data)).digest('hex');
  }

  add(data) {
    const block = {
      timestamp: new Date(),
      data,
    };

    const hashData = { block };
    if (this.blocks.length > 0) {
      hashData.previousHash = this.blocks[this.blocks.length - 1].hash;
    }
    block.hash = this.hash(hashData);

    this.blocks.push(block);
  }

  verify() {
    for (const index in this.blocks) {
      const block = this.blocks[index];

      const hashData = { block: { timestamp: block.timestamp, data: block.data }};
      if (index > 0) {
        hashData.previousHash = this.blocks[index - 1].hash;
      }
      const hash = this.hash(hashData);

      if (block.hash !== hash) {
        return false;
      }
    }
    return true;
  }
}

Consense of the first reviews and feedbacks: It's not a blockchain, it's a merkle tree what I did. A blockchains needs to be centralized with the networking and syncing parts. :)