Create Blockchain With Node.js. Learn by creating your own blockchain… | by Abhishek Chauhan | Apr, 2022

blockchain improvement | picture credit score: Tezos

On this chapter, we are going to dive deep into the code, and the examples on this chapter are easy in nature and meant for studying functions. They gives you a greater understanding of blockchain and the weather which can be wanted to realize a completely working prototype of a blockchain.

  1. Making a fundamental P2P community
  2. Sending and receiving blocks
  3. Registering miners and creating new blocks
  4. Organising a name-value database, LevelDB
  5. Making a private-public pockets
  6. Creating an API
  7. Making a command-line interface

Peer-to-peer (P2P) is a kind of pc community that makes use of a distributed structure. Every peer or node shares the workload and is the same as the opposite friends, that means there shouldn’t be any privileged peer.

Create a folder and identify it Blockchain.

Your code wants to search out and join friends, deploy servers which can be used to find different friends, and get an out there TCP port. That’s achieved by using these three libraries:

  • discovery-swarm: Used to create a community swarm that makes use of discovery-channel to search out and join friends
  • dat-swarm-defaults: Deploys servers which can be used to find different friends
  • get-port: Will get out there TCP ports

To put in these libraries, run this command:

npm set up crypto discovery-swarm dat-swarm-defaults get-port@5.1.1 --save

Now that the libraries are put in, create a file and identify it p2p.js and write the next code. Alternatively, you could possibly simply copy the gist,


Open two Terminal situations and navigate to the placement of the library. Run the next command in each terminals:

node p2p.js
output p2p

As you’ll be able to see above, the community generated a random peer ID to your machine and picked a random port using the invention libraries you put in. Then the code was in a position to uncover different friends on the community and ship and obtain messages to and from these friends. You at the moment are linked on a P2P community with different customers.

Creating Genesis Block and Sharing Blocks

The Block object is just not the identical for each blockchain. Totally different blockchains make the most of several types of Block objects; you can be utilizing a Block object much like bitcoin.

block stream

the Block object comprises the next properties:

  • index: GenesisBlock is our first block, we assign the block index with the worth of 0.
  • txns: That is the uncooked transaction within the block. I don’t need to deal with simply cryptocurrencies on this chapter, so consider this as any kind of information you need to retailer.

Included within the Block object is the BlockHeader object, which comprises the next properties:

  • Model: On the time of writing, there are 4 block variations. Model 1 is the genesis block (2009), and model 2 is a smooth fork of bitcoin core 0.7.0 (2012). Model 3 blocks had been a smooth fork of bitcoin core 0.10.0 (2015). Model 4 blocks are BIP65 in bitcoin core 0.11.2 (2015).
  • Earlier block header hash: That is an SHA-256 (Safe Hash Algorithm) hash perform of the earlier block’s header. It ensures that the earlier block can’t be modified as this block must be modified as nicely.
  • Merkle root hash: A Merkle tree is a binary tree that holds all of the hashed pairs of the tree.
  • Time: That is the Unix epoch time when the miner began hashing the header.

As you recall, bitcoin additionally features a problem property for the miners that will get recalculated each 2,016 blocks. Right here you gained’t use the nBits and nounce params, as you aren’t doing PoW.

  • nounce: The nonce in a bitcoin block is a 32-bit (4-byte) area whose worth is adjusted by miners in order that the hash of the block will probably be lower than or equal to the present goal of the community.
  • nBits: This refers back to the goal. The goal is a 256-bit quantity and is inversely proportional to the problem. It’s recalculated each 2,016 blocks.

By way of P2P communication, the stream of blocks between every peer on the P2P community consists of requesting the most recent block from a peer on the community after which receiving a block request.

Stream diagram of P2P communications requesting newest block and receiving newest block

Now that you simply perceive the structure and the stream of blocks within the P2P community, subsequent, you can be sending and requesting blocks.

P2P community sending block

Setting Up a Block Class and Chain Library

The blockchain consists of two information: block.jsand chain.js. The file block.js will maintain the block class object, and chain.js would be the glue with strategies to deal with the interactions with the blocks. By way of the Block object, you can be creating properties much like the properties that bitcoin core holds. Check out block.js file consists of Block and BlockHeader objects.


As you’ll be able to see, chain.js comprises the primary block, which is known as the genesis block, in addition to a technique to obtain the whole blockchain object, add a block, and retrieve a block. Notice that you can be including a library known as second to save lots of the time in a Unix time format in your chain.js library. To take action, set up second with npm.

npm set up second --save

Now create the chain.js :


Now we’ve obtained a block object that’s included in chain.js. Our library can create a genesis block and add a block to your blockchain object. Additionally, we’ll be capable of ship and request blocks. Now, use the chain.js in p2p.js :


At this level, now we have a fundamental P2P community, and we’re in a position to join friends within the community, create a genesis block, and ship and obtain blocks. The following step is with the ability to generate new blocks.

We’ll take an method of proof of stake (PoS) the place you belief every miner to generate blocks. Every peer will register as a miner and can take a flip to mine a block.

Your blockchain handles mining utilizing a easy PoS mechanism

To automate the method of producing a block each X variety of minutes, you should use a Node.js library known as cron, which is analogous to the Linux library that automates duties. To put in the cron open-source library, run the next command:

npm set up cron --save

Subsequent, in your p2p.js file, you’ll create two variables to maintain observe of the registered miners in addition to who mined the final block so you’ll be able to assign the subsequent block to the subsequent miner.

let registeredMiners = [];
let lastBlockMinedBy = null;

You’re additionally going so as to add two messages varieties.

let MessageType =  
REQUEST_BLOCK: ‘requestBlock’,
RECEIVE_NEXT_BLOCK: ‘receiveNextBlock’,
RECEIVE_NEW_BLOCK: ‘receiveNewBlock’, REQUEST_ALL_REGISTER_MINERS: ‘requestAllRegisterMiners’,
REGISTER_MINER: ‘registerMiner’

Earlier than you register your friends as miners, you’ll request to obtain all the present registered miners within the community, after which you’ll add your peer as a miner in a registeredMiners object. You do this by working a timer to replace your miners each 5 seconds.

setTimeout(perform() writeMessageToPeers(MessageType.REQUEST_ALL_REGISTER_MINERS, null); , 5000);

Now, that has an automatic timeout command that may level to a handler to replace the checklist of registered miners you may as well automate a command to register your peer as a miner;

setTimeout(perform() registeredMiners.push(myPeerId.toString(‘hex’));
console.log(‘ — — — — — Register my miner — — — — — — — ‘); console.log(registeredMiners); writeMessageToPeers(MessageType.REGISTER_MINER, registeredMiners); console.log(‘ — — — — — Register my miner — — — — — — — ‘);
, 7000);

In your swap command, modify the code to have the ability to set handlers for incoming messages concerning the registrations of miners. We need to maintain observe of the registered miners in addition to deal with a message as soon as a brand new block is mined.

console.log(‘ — — — — — -REQUEST_ALL_REGISTER_ MINERS — — — — — — — ‘ +;
writeMessageToPeers(MessageType.REGISTER_MINER, registeredMiners); registeredMiners = JSON.parse(JSON.stringify(message. information)); console.log(‘ — — — — — -REQUEST_ALL_REGISTER_ MINERS — — — — — — — ‘ +;
case MessageType.REGISTER_MINER:
console.log(‘ — — — — — -REGISTER_MINER — — — — — — — ‘ +;
let miners = JSON.stringify(message.information);
registeredMiners = JSON.parse(miners);
console.log('----------- REGISTER_MINER------------- ' +;

You additionally have to unregister a miner as soon as a reference to the miner is closed or misplaced.

console.log(`Connection $seq closed, peerId: $peerId`); if (friends[peerId].seq === seq)  
delete friends[peerId];
console.log(‘ — — registeredMiners earlier than: ‘ + JSON.stringify(registeredMiners));
let index = registeredMiners.indexOf(peerId);
if (index > -1)
registeredMiners.splice(index, 1);
console.log(‘ — — registeredMiners finish: ‘ +


Mine a brand new block

Versus bitcoin, which generates a block each 10 minutes, your blockchain will probably be improved and can generate a block each 30 seconds. To realize that, you already put in the open-source cron library for Node.js. The cron library works the identical because the Linux cron. You’ll be able to make the most of the cron library to set how usually to name the identical code once more, which will probably be used to name your miners each 30 seconds.

To take action, first embody the library in your code’s import assertion on prime of the p2p.js file. Subsequent, you set a cronjob to run each 30 seconds, and job.begin(); will begin the job,

After including all of the above features your p2p.js file will appear to be this:


A LevelDB database shops name-value pairs in what is known as a level-up and level-down vogue. It is a perfect possibility for blockchain networks. Actually, bitcoin makes use of LevelDB to retailer not solely block info but in addition transaction info. To make use of it, set up stage with npm.

npm set up stage --save

Subsequent, make a listing the place you can be saving the database.

mkdir db

Now you can implement the database. In chain.js, add some code to save lots of your block within the LevelDB database.


Lastly, in your p2p.js file, all that you must do is create a database when you begin the code.

including createDb in p2p.js

In cryptocurrency, a pockets is critical with a purpose to reward miners for producing blocks in addition to to have the ability to create transactions and ship transactions. On this part, you’ll create a pockets. It’s worthwhile to create a mixture of private and non-private keys not simply to authenticate a consumer however so you’ll be able to retailer and retrieve information that the consumer owns. You’ll create a pockets with private and non-private keys.

You can be utilizing the elliptic-curve cryptography library implementation to generate private-public key combos. Notice that the elliptic-curve library makes use of secp256k1 because the ECDSA curve algorithm. To put in it, run the next command,

npm i elliptic --save

Create a brand new file pockets.js and duplicate the next code,

Subsequent, create a pockets listing to retailer the personal key and run the script. The code will initialize the script and create your public key.

mkdir pockets
node pockets.js
cat pockets/private_key
output personal key

Bear in mind to remark out final strains 32 to 34 of pockets.jsas a result of within the subsequent, you’ll create an API to have the ability to create your keys by way of the browser.

The following step is creating an software program interface (API) to have the ability to entry the code you write. This is a crucial a part of a blockchain, as you need to entry your blocks and pockets or every other P2P community operation utilizing an HTTP service.

You’ll set up categorical and body-parser. These libraries will mean you can create a server and show pages within the browser.

npm set up categorical body-parser — save

Now open your p2p.js file and comply with alongside,

To name your companies, run the P2P community,

node p2p.js
p2p.js output

Now, open a browser and name the API,

calling /blocks API within the browser

For the final step on this chapter, you can be making a command-line interface (CLI). The CLI is required to have the ability to simply entry the companies you created.

Subsequent, set up the libraries you can be using to run guarantees, run the async perform, add colours to the console, and retailer cookies.

npm i babel-polyfill async update-notifier handlebars colours nopt --save

Create a brand new listing cliand inside one other cmds for instructions

mkdir cli
cd cli
mkdir cmds
contact block.js assist.js model.js pockets.js

Within the block.js, you can be setting two instructions: get and all,

block.js cli

As you’ll be able to see, the pockets.js will embody the get and all strategies to level to a curl command to run the HTTP service name,

pockets.js cli

Equally, we are going to do for others please comply with this link. Copy codes from the given hyperlink.

Now, create a listing bin and add cli.js ,

Now that you’ve got your instructions arrange, you’ll be able to add your CLI to the bash_profile as an alias to have the ability to run the CLI from any path location.

nano .bash_profilealias cli='node /<location>/Blockchain/bin/cli.js'

Press ctrl+o to save lots of and ctrl+X to exit, then run bash_profile,

. ~/.bash_profile

Hurray!! Our command-line interface is prepared 😃, let’s take a look at it,

node p2p.js

Open one other terminal and run,

cli block --get [port] 1 
cli block –all [port]
cli pockets --create [port]
cli interface output

Congrats👏 now we have created our personal blockchain 🔥🔥🔥🔥

On this article, now we have lined how one can create your very personal fundamental P2P blockchain community; you had been in a position to ship and obtain messages and embody blocks in these messages; you had been in a position to register and unregister miners and implement a easy PoS consensus mechanism; you created new blocks and despatched them between the friends; you additionally arrange a name-value LevelDB database to retailer blocks; you continued and created a pockets that consists of private-public key pairs. Lastly, you created methods to speak along with your P2P community by way of API companies and the CLI.

Need to Join?For the complete code go to and should you prefer it, comply with me on GitHub:

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