Nodejs builds blockchain

Node.js is a JavaScript runtime environment based on event-driven, asynchronous I/O. With the rise of digital currency and blockchain technology, Node.js has gradually become an important tool for developing blockchain applications. Building a blockchain based on Node.js can make it more open, decentralized, safe and reliable. This article will introduce how to use Node.js to build your own blockchain.

1. What is blockchain

Blockchain is a distributed, decentralized ledger technology that can be used to record transactions and ensure the authenticity of transactions in the network. and security. Each block of the blockchain contains the hash value of the previous block, forming an immutable data structure.

2. The relationship between Node.js and blockchain

Node.js can be used to build back-end services for blockchain applications, providing data interaction, transaction verification, Data storage and other functions. The power of Node.js lies in its asynchronous I/O mechanism and event-driven model, which can handle a large number of concurrent requests and facilitate expansion and upgrade.

3. Build Node.js blockchain application

1. Install Node.js

First you need to install the Node.js environment, in Node.js Download the installation package of the corresponding version from the official website and install it. After the installation is complete, you can enter the node -v command in the terminal to check the version of Node.js.

2. Install necessary packages

There are many open source packages in Node.js that can be used to build blockchain applications, such as crypto-js, bitcoinjs-lib, web3 .js etc. You need to use the npm command line tool to install these packages, for example:

npm install crypto-js

After the installation is complete, these packages can be introduced in the JavaScript code through the require() function.

3. Building back-end services

Node.js can use the Express framework to build back-end services to achieve data interaction between nodes. First you need to install Express, enter in the terminal:

npm install express

To build a simple Express application, you can write the following code in the app.js file:

const express = require('express')
const app = express()

app.get('/', function (req, res) {
  res.send('Hello World!')
})

app.listen(3000, function () {
  console.log('Example app listening on port 3000!')
})

Among them, app.get( ) method indicates that when a GET request accesses the root directory, a "Hello World!" message is returned to the client. The app.listen() method specifies that the Express application listens on port 3000.

4. Implementing Blockchain

Using Node.js can easily implement a simple blockchain. The code is as follows:

const SHA256 = require('crypto-js/sha256');

class Block{
    constructor(index, timestamp, data, previousHash = ''){
        this.index = index;
        this.timestamp = timestamp;
        this.data = data;
        this.previousHash = previousHash;
        this.hash = this.calculateHash();
    }

    calculateHash(){
        return SHA256(this.index + this.previousHash + this.timestamp + JSON.stringify(this.data)).toString();
    }
}

class Blockchain{
    constructor(){
        this.chain = [this.createGenesisBlock()];
    }

    createGenesisBlock(){
        return new Block(0, "01/01/2020", "Genesis 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(){
        for(let 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 myBlockchain = new Blockchain();
myBlockchain.addBlock(new Block(1, "02/01/2020", { amount: 4 }));
myBlockchain.addBlock(new Block(2, "03/01/2020", { amount: 8 }));

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

Among them, the Block class represents the basic attributes of the block, including index, timestamp, data, hash value of the previous block, and hash value of this block. The calculateHash() method calculates the hash value of the block based on these attributes. The Blockchain class represents the entire blockchain, including methods to create initial blocks, obtain the latest blocks, add new blocks, and verify whether the entire blockchain is legal.

Using this code, you can implement a simple blockchain, including the initial block, two new blocks, and a method to verify whether the entire chain is legal.

4. Conclusion

This article introduces how to use Node.js to build your own blockchain. As a high-performance, highly scalable back-end service tool, Node.js has broad application prospects in blockchain applications. Using Node.js can better realize the openness, decentralization, security and reliability of the blockchain.

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