Question

implement the block chain coding based on the following video. Submit the code, and a separate explanation how the code works.

https://youtu.be/zVqczFZr124

Answer 1

class Block{

//Structure of the block what information a block should coantain

constructor(index,timestamp,data,previousHash=' ')

this.index=index;;

this.timestamp=timestamp;

this.data=data;

this.previousHash=previousHash;

this.hash=this.calculate();

calculateHash(){

return SHA256( this.index+this.timestamp+this.previousHash+JSON.stringfy(this.data)).toString();

}

class Blockchain{

constructor(){

this.chain=[this.createGenesisBlock()];

}

// the first block in block chain is called genesis block

createGenesisBlock(){

new Block(0,"16/11/2018","Genesis Block","0");

}

getLatestBlock{

return this.chain[this.chain.lenght-1];

}

addBlock{

newBlock.previousHash=this.getLatestBlock().hash;

newBlock.hash=newBlock.calculateHash();

this.chain.push(newBlock);

}

//Checking if the chain in valid or not (previous hash value in current block ) should be equal to (hash value in previous // // // block) . If not then that block is referring to some other block chain.

isChainValid(){

for(i=1;i<this.chain.length; i++)

const currentBlock = this.chain[i];

const previousBlock = this.chain[i-1];

if(currentBlock.hash != currentBlock.calculatehash()){

return false;

}

if(currentBlock.previousHash != previousBlock.hash()){

return false;

}

return true;

}

let coin=new Blockchain();

coin.addBlock(new Block(1, "17/11/2017", {amount:4} ));

coin.addBlock(new Block(1, "18/11/2017", {amount: 5 } ));

console.log(JSON.stringify(coin, null , 4));

Notes:

Run the above script as node chain.js

See, Every block in block chain has a hash function and hash function for the previous block . So a newly created block is attached to the previous block and thus chain keeps on growing.

First Block has no previous block so : That is called genesis block

Also if a new block is created you cannot delete that block.