main.js

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//CREATION OF A BLOCKCHAIN
//SIMPLE DEFINITION OF BLOCKCHAIN: A distributed database that maintains a continuously growing list of ordered records.
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//"The block needs to be hashed to keep the integrity of the data.     /////////////////////
//A SHA-256 is taken over the content of the block.                    /////////////////////
//It should be noted that this hash has nothing to do with “mining”,   /////////////////////
//since there is no Proof Of Work problem to solve."                   /////////////////////
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//BELOW WE ARE IMPORTING SHA256 LIBRARY:
const SHA256 = require('crypto-js/sha256');
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//CLASS block STARTS FROM HERE AND IT'LL INCLUDE THE CALCULATION OF GENESIS-BOCK/1ST-BLOCK AS WELL:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
class block { //WE'LL BEGIN BY MAKING A CLASS OF BLOCK:
    constructor( //IN A CONSTRUCTOR, WE'RE ADDING THE PROPERTIES OF A BLOCK WE NEED TO MAKE A BLOCKCHAIN:
        index, //index tells where the block sits on the chain: means its position on the chain. 
        timeStamp, //timeStamp tell the time when the block was created: means its date of creation.
        data, //data could contain any type of information e.g; in case of currency--it can contain details of transaction, sender, & receiver.
        previousHash = '' //previousHash contains the string (unique ID) of the block, that insures the integrity of the blockchain, otherwise the block will be invalid.
    ) { //NOW WE KEEP TRACK OF ABOVE PROPERTIES BY USING this. STATEMENT. (SUMMARY: means, we cloned them for a reuse!)
        this.index = index;
        this.timeStamp = timeStamp;
        this.data = data;
        this.previousHash = previousHash;
        this.hash = this.calculateHash(); //hash will contain the hash of our block, and will need to be calculated, hence we'll be needing a way to calculate it.
        //above this.hash func is equals to this.calculateHash() so, the hash of the properties of the block can be calculated by the method/func on the Ln26 func section.  
    }
    //NOW WE'RE MAKING A METHOD/FUNC THAT WILL CALCULATE THE HASH OF THE BLOCK:
    //SUMMARY: means, it'll calculate the hash func, for that we'll need the properties (tracked/cloned properties, we made for reuse) of the block, and then it'll generate a new Hash (unique ID) for the block.
    //BEFORE CALCULATING, WE'LL NEED HASH FUNC/HASH-NUMBER, THAT WILL BE PROVIDED BY A LIBRARY CALLED crypto-js (npm). WE'LL INSTALL IT IN OUR CODE THROUGH TERMINAL TO GET THOSE HASH FUNCS.
    calculateHash() {
        //now we'll return/declare here the sha256 hash of our properties:
        //this.index + this.SoOn declares that this info/parameters are passing to the hash function(20) & calculateHash(Ln26) function for the calculation. 
        return SHA256(this.index + this.timeStamp + this.previousHash + JSON.stringify(this.data)).toString(); //to make it look good like a database, we have used JSON.stringify, it'll make the data property look good like its in an array. and .toString will take the output of the sha256, and will cast it to a string, otherwise we'll get an object from the library we're using.
        //AFTER ABOVE CODE LINE, WE'LL GO BACK TO OUR HASH FUNCTION(Ln20) WE WROTE IN THE CONSTRUCTOR WITH NO PARAMETER. WE'LL DECLARE IT THIS CALC METHOD(26) SO IT CAN GENERATE THE HASH NO.
    }
}
//CLASS block ENDS HERE AND CALCULATION SECTIONS AS WELL! //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

//2ND CLASS FOR BLOCKCHAIN THAT WILL START THE CHAIN-FORMING-SYSTEM BY CREATING NEW BLOCKS, STARTS FROM HERE::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
//NOW WE'RE CREATING A CLASS FOR BLOCKCHAIN:
class blockChain { //we'll here again give it a constructor:
    constructor() { //this constructor will be responsible for initializing our blockchain, hence we'll give a property "chain" in this class which will be an array of blocks.
        this.chain = [this.createGenesisBlock()]; //after providing info in the below createGenesisBlock we declared that func on Ln39 in this.chain property, hence it could have the info to put into set of arrays.
        //THE 1ST BLOCK ON THE BLOCKCHAIN IS CALLED A GENESIS BLOCK, WHICH WE'LL BE CREATING MANUALLY, HENCE WE'LL MAKE ANOTHER METHOD FOR IT, IN THIS CLASS, OUTSIDE OF THIS CONSTRUCTOR:
    }
    createGenesisBlock() { //Genesis block will return new block:
        //we're gonna make new block in the blockchain from the 1st block we created at Ln9 which is known as the Genesis Block.
        return new block(0, "01/01/2022", "Account User: Uswa R. Balance: 1 Dodge Coin", "0"); //here we put the info into the 1st block "Genesis". It contains property variables like index = 0, date (timeStamp) = 01/01/2022, data = could be anything, & previousHash = which doesn't exist on its own or before, hence could be any random number/data.
        //AFTER ABOVE CODE LINE OR DECLARATION OF INPUT IN THE PARAMETERS, WE'LL HEAD UPWARDS TO OUR CONSTRUCTOR OF BLOCKCHAIN WHERE WE MADE A PROPERTY CALLED CHAIN, AND WE'LL DECLARE OUR ITS BELOW createGenesisBlock function/method, SO IT CAN HAVE THE DATA WE PROVIDED IN ITS ARRAY. 
    }
    //BELOW METHOD/FUNC WILL BE USEFUL FOR FUTURE:
    //getLatestBlock method will make the latest chain, hence we're giving this.chain property below:
    getLatestBlock() {
        return this.chain[this.chain.length - 1]; //to return its last element, we've used .length here with -1.
    }
    //-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
    //addBlock method will receive a new block or let's say: connects to previous block, make a new chain with it to connect to the latest block, to make it a block-chain:
    addBlock(newBlock) {
        //now the addBlock method will generate new blocks but it'll require the previousHash to get data from, hence we're using previousHash below to continue the formation of blockchain:
        newBlock.previousHash = this.getLatestBlock().hash; //since new/latest block formation requires previous block's data, hence we used previousHash but to put this previous hash-data into latest/new block we have to use latestBlock method, and .hash to tell our method that we need a new hash ID formation not the whole data.
        //now below, to re-calculate the hash to get a new hash unique ID for our latest/new block, for in-case, if any property from our 1st-block/genesis-block or class block at Ln9 (from constructor properties, (not reusable properties)), will be changed or tampered then, new block's ID will be new and unique.
        newBlock.hash = newBlock.calculateHash(); //now, we told the addBlock method after declaring that it'll need to generate a new unique hash ID from previous hash, and then it has to re-calculate it from calculateHash() method, which is our hash calculator. 
        this.chain.push(newBlock); //now we're pushing the re-calculated block with a new unique hash ID to the chain, with the help of .push.  
    }
}    
//2ND CLASS OF BLOCKCHAIN ENDS RIGHT HERE__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________


//NOW TO TEST ALL THE CODE WE WROTE ABOVE, WE'LL CREATE AN 'INSTANCE' OF OUR BLOCKCHAIN:
//DEFINITION: An instance is an object containing data and behavior described by the class.
//We are making new block here that will derive from the genesis block.
let uswaSBlockChain = new blockChain(); //here we made a variable and named it uswaSBlockChain, then referred the variable to blockChain(Ln37) method, where the chain formation step takes place.
uswaSBlockChain.addBlock(new block(1, "04/01/2022", "Account User: Uswa R. Balance: 3 Dodge Coin", "0")); //now here we're giving the new block its details/info/data (index, timeStamp, previousHash, & data), and referring it to the addBlock method.
uswaSBlockChain.addBlock(new block(2, "07/04/2022", "Account User: Uswa R. Balance: 6 Dodge Coin", "0")); //now here we're giving the new block its details/info/data (index, timeStamp, previousHash, & data), and referring it to the addBlock func.
//we made 2 new blocks, that will derive from the Genesis Block, thus there will be total 3 blocks of blockchain.
//FORMATION OF NEW BLOCK IN THE BLOCKCHAIN ENDS HERE.
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console.log(uswaSBlockChain); //here we run it without JSON.Stringify to see in actual blockchain logic and visualization.

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//WE HAVE SUCCESSFULLY CREATED A BLOCKCHAIN!
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