├── .gitignore
├── README.md
├── blockchain.js
└── package.json


/.gitignore:
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 1 | # Logs
 2 | logs
 3 | *.log
 4 | npm-debug.log*
 5 | yarn-debug.log*
 6 | yarn-error.log*
 7 | 
 8 | # Runtime data
 9 | pids
10 | *.pid
11 | *.seed
12 | *.pid.lock
13 | 
14 | # Directory for instrumented libs generated by jscoverage/JSCover
15 | lib-cov
16 | 
17 | # Coverage directory used by tools like istanbul
18 | coverage
19 | 
20 | # nyc test coverage
21 | .nyc_output
22 | 
23 | # Grunt intermediate storage (http://gruntjs.com/creating-plugins#storing-task-files)
24 | .grunt
25 | 
26 | # Bower dependency directory (https://bower.io/)
27 | bower_components
28 | 
29 | # node-waf configuration
30 | .lock-wscript
31 | 
32 | # Compiled binary addons (http://nodejs.org/api/addons.html)
33 | build/Release
34 | 
35 | # Dependency directories
36 | node_modules/
37 | jspm_packages/
38 | 
39 | # Typescript v1 declaration files
40 | typings/
41 | 
42 | # Optional npm cache directory
43 | .npm
44 | 
45 | # Optional eslint cache
46 | .eslintcache
47 | 
48 | # Optional REPL history
49 | .node_repl_history
50 | 
51 | # Output of 'npm pack'
52 | *.tgz
53 | 
54 | # Yarn Integrity file
55 | .yarn-integrity
56 | 
57 | # dotenv environment variables file
58 | .env
59 | 
60 | 


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/README.md:
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1 | # Blockgeeks: Build Your Own Blockchain with JavaScript
2 | Code that shows how to build your own Bitcoin-alike blockchain with JavaScript.
3 | 
4 | I want to thank [Savjee](https://github.com/SavjeeTutorials) for making this article possible.


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/blockchain.js:
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  1 | const SHA256 = require("crypto-js/sha256");
  2 | 
  3 | class Transaction{
  4 |     constructor(fromAddress, toAddress, amount){
  5 |         this.fromAddress = fromAddress;
  6 |         this.toAddress = toAddress;
  7 |         this.amount = amount;
  8 |     }
  9 | }
 10 | 
 11 | class Block {
 12 |     constructor(timestamp, transactions, previousHash = '') {
 13 |         this.previousHash = previousHash;
 14 |         this.timestamp = timestamp;
 15 |         this.transactions = transactions;
 16 |         this.hash = this.calculateHash();
 17 |         this.nonce = 0;
 18 |     }
 19 | 
 20 |     calculateHash() {
 21 |         return SHA256(this.previousHash + this.timestamp + JSON.stringify(this.transactions) + this.nonce).toString();
 22 |     }
 23 | 
 24 |     mineBlock(difficulty) {
 25 |         while (this.hash.substring(0, difficulty) !== Array(difficulty + 1).join("0")) {
 26 |             this.nonce++;
 27 |             this.hash = this.calculateHash();
 28 |         }
 29 | 
 30 |         console.log("BLOCK MINED: " + this.hash);
 31 |     }
 32 | }
 33 | 
 34 | 
 35 | class Blockchain{
 36 |     constructor() {
 37 |         this.chain = [this.createGenesisBlock()];
 38 |         this.difficulty = 4;
 39 |         this.pendingTransactions = [];
 40 |         this.miningReward = 100;
 41 |     }
 42 | 
 43 |     createGenesisBlock() {
 44 |         return new Block(Date.parse("2017-01-01"), [], "0");
 45 |     }
 46 | 
 47 |     getLatestBlock() {
 48 |         return this.chain[this.chain.length - 1];
 49 |     }
 50 | 
 51 |     minePendingTransactions(miningRewardAddress){
 52 |         let block = new Block(Date.now(), this.pendingTransactions, this.getLatestBlock().hash);
 53 |         block.mineBlock(this.difficulty);
 54 | 
 55 |         console.log('Block successfully mined!');
 56 |         this.chain.push(block);
 57 | 
 58 |         this.pendingTransactions = [
 59 |             new Transaction(null, miningRewardAddress, this.miningReward)
 60 |         ];
 61 |     }
 62 | 
 63 |     createTransaction(transaction){
 64 |         this.pendingTransactions.push(transaction);
 65 |     }
 66 | 
 67 |     getBalanceOfAddress(address){
 68 |         let balance = 0;
 69 | 
 70 |         for(const block of this.chain){
 71 |             for(const trans of block.transactions){
 72 |                 if(trans.fromAddress === address){
 73 |                     balance -= trans.amount;
 74 |                 }
 75 | 
 76 |                 if(trans.toAddress === address){
 77 |                     balance += trans.amount;
 78 |                 }
 79 |             }
 80 |         }
 81 | 
 82 |         return balance;
 83 |     }
 84 | 
 85 |     isChainValid() {
 86 |         for (let i = 1; i < this.chain.length; i++){
 87 |             const currentBlock = this.chain[i];
 88 |             const previousBlock = this.chain[i - 1];
 89 | 
 90 |             if (currentBlock.hash !== currentBlock.calculateHash()) {
 91 |                 return false;
 92 |             }
 93 | 
 94 |             if (currentBlock.previousHash !== previousBlock.hash) {
 95 |                 return false;
 96 |             }
 97 |         }
 98 | 
 99 |         return true;
100 |     }
101 | }
102 | 
103 | let codeCoin = new Blockchain();
104 | codeCoin.createTransaction(new Transaction('address1', 'address2', 100));
105 | codeCoin.createTransaction(new Transaction('address2', 'address1', 50));
106 | 
107 | console.log('\n Starting the miner...');
108 | codeCoin.minePendingTransactions('michiel-address');
109 | 
110 | console.log('\nBalance of Michiel is', codeCoin.getBalanceOfAddress('michiel-address'));
111 | 
112 | console.log('\n Starting the miner again...');
113 | codeCoin.minePendingTransactions('michiel-address');
114 | 
115 | console.log('\nBalance of Michiel is', codeCoin.getBalanceOfAddress('michiel-address'));
116 | 


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/package.json:
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 1 | {
 2 |   "name": "build-your-own-blockchain",
 3 |   "main": "blockchain.js",
 4 |   "scripts": {
 5 |     "start": "node blockchain.js"
 6 |   },
 7 |   "dependencies": {
 8 |     "crypto-js": "^3.1.9-1"
 9 |   }
10 | }


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