Added js blockchain class

.gitignore

@@ -102,3 +102,5 @@ ENV/
 
 # PyCharm
 .idea/
+
+node_modules/

js/blockchain.js

@@ -0,0 +1,95 @@
+const crypto = require("crypto");
+
+
+class Blockchain {
+    constructor() {
+        this.chain = [];
+        this.pendingTransactions = [];
+        this.newBlock();
+    }
+
+    /**
+     * Creates a new block containing any outstanding transactions
+     *
+     * @param previousHash: the hash of the previous block
+     * @param nonce: the random string used to make this block hash satisfy the difficulty requirements
+     */
+    newBlock(previousHash, nonce = null) {
+        let block = {
+            index: this.chain.length,
+            timestamp: new Date().toISOString(),
+            transactions: this.pendingTransactions,
+            previousHash,
+            nonce
+        };
+
+        block.hash = this.hash(block);
+
+        console.log(`Created block ${block.index}`);
+
+        // Add the new block to the blockchain
+        this.chain.push(block);
+
+        // Reset pending transactions
+        this.pendingTransactions = [];
+    }
+
+    /**
+     * Generates a SHA-256 hash of the block
+     * @param block
+     */
+    hash(block) {
+        const blockString = JSON.stringify(block, Object.keys(block).sort());
+        return crypto.createHash("sha256").update(blockString).digest("hex");
+    }
+
+    /**
+     * Gets the last block in the chain
+     */
+    lastBlock() {
+        return this.chain.length && this.chain[this.chain.length - 1];
+    }
+
+    /**
+     * Determines if a hash begins with a "difficulty" number of 0s
+     *
+     * @param hashOfBlock: the hash of the block (hex string)
+     * @param difficulty: an integer defining the difficulty
+     */
+    powIsAcceptable(hashOfBlock, difficulty) {
+        return hashOfBlock.slice(0, difficulty) == "0".repeat(difficulty);
+    }
+
+    /**
+     * Generates a random 32 byte string
+     */
+    nonce() {
+        return crypto.createHash("sha256").update(crypto.randomBytes(32)).digest("hex");
+    }
+
+    /**
+     * Proof of Work mining algorithm
+     *
+     * We hash the block with random string until the hash begins with
+     * a "difficulty" number of 0s.
+     *
+     * @param _block: the block to be mined (defaults to the last block)
+     * @param difficulty: the mining difficulty to use
+     */
+    proofOfWork(_block = null, difficulty = 4) {
+        const block = _block || this.lastBlock();
+
+        while (true) {
+            block.nonce = this.nonce();
+            if (this.powIsAcceptable(this.hash(block), difficulty)) {
+                console.log("We mined a block!")
+                console.log(` - Block hash: ${this.hash(block)}`);
+                console.log(` - nonce:      ${block.nonce}`);
+                return block;
+            }
+        }
+    }
+}
+
+const blockchain = new Blockchain();
+blockchain.proofOfWork(null, 5);

js/package.json

@@ -0,0 +1,17 @@
+{
+  "name": "blockchain",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "author": "",
+  "license": "ISC",
+  "dependencies": {
+    "nodemon": "^1.19.0"
+  },
+  "scripts": {
+    "dev": "nodemon blockchain.js"
+  }
+}