Skip to content

Instantly share code, notes, and snippets.

@joeynimu
Last active Sep 11, 2017
Embed
What would you like to do?
Really simple demonstration of how block chain works.
// you need to first run `npm i --save crypto-js`
const SHA256 = require('crypto-js/sha256');
class Block{
constructor(index, data, previsousHash='', date = new Date()){
// takes in the following params; index: number, timestamp: string/object, data: object and previousHash: string
this.index = index,
this.timestamp = this.formatTimeStamp(),
this.data = data,
this.previsousHash = this.calculateHash(),
this.date = date
}
calculateHash(){
return SHA256(this.index + this.previousHash + this.timestamp + JSON.stringify(this.data)).toString();
}
getTime(){
let date = new Date();
return {
hours: date.getHours(),
minutes: date.getMinutes(),
seconds: date.getSeconds(),
milliseconds: date.getMilliseconds()
}
}
formatTimeStamp(){
let date = new Date();
let day = date.getDay();
let month = date.getMonth();
let year = date.getFullYear();
return {
day: day,
month: month,
time: this.getTime(),
year: year
}
}
}
class BlockChain{
constructor(){
this.chain = [this.createGenesisBlock()]
}
createGenesisBlock(){
return new Block(0, 'Start Block', '0');
}
getLatestBlock(){
return this.chain[this.chain.length - 1];
}
addBlock(newBlock){
newBlock.previousHash = this.getLatestBlock().hash;
newBlock.hash = newBlock.calculateHash();
this.chain.push(newBlock);
}
isChainValid(){
// loops through all the chains doing some checks
for(let i = 1; i < this.chain.length; i++){
let currBlock = this.chain[i];
let prevBlock = this.chain[i - 1];
// it currentHash doesn't match the calculateHash, chain is invalid
if(currBlock.hash !== currBlock.calculateHash()){
return false;
}
// compare previousHash from currentblock doesn't match that from previous block hash chain is invalid
if(currBlock.previousHash !== prevBlock.hash){
return false;
}
}
// else chain is valid
return true;
}
}
let bitCoin = new BlockChain();
bitCoin.addBlock(new Block(1, {amount: 4}));
bitCoin.addBlock(new Block(2, {amount: 10}));
console.log('First time validation before inteferance: ' + bitCoin.isChainValid());
bitCoin.chain[1].data = {amount: 10};
bitCoin.chain[1].hash = bitCoin.chain[1].calculateHash();
console.log('After inteferance: ' + bitCoin.isChainValid()); //this returns false
// console.log(JSON.stringify(bitCoin, null, 4)); //uncomment this to see the full bitCoin object
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment