Blockchain implementation in JS by @ssaurel

Blockchain.js

class Blockchain {
 constructor(difficulty) {
    this.difficulty = difficulty;
    this.blocks = [];
    // Add Genesis Block
    var genesisBlock = new Block(0, null, Date.now(), "Genesis block");
    genesisBlock.mineBlock(this.difficulty);
    this.blocks.push(genesisBlock);
 }
}

Blockchain.prototype.newBlock = function (data) {
 var latestBlock = this.blocks[this.blocks.length - 1];
 return new Block(latestBlock.index + 1, latestBlock.hash, 
                   Date.now(), data);
}

Blockchain.prototype.addBlock = function(block) {
 block.mineBlock(this.difficulty);
 this.blocks.push(block);
}

Blockchain.prototype.isFirstBlockValid = function() {
 var firstBlock = this.blocks[0];
 
 if (firstBlock.index != 0)
   return false;
   
 if (firstBlock.previousHash != null)
   return false;
   
 if (firstBlock.hash == null ||
       calculateHash(firstBlock) != firstBlock.hash)
    return false;
    
 return true; 
}

Blockchain.prototype.isValidBlock = function (block, previousBlock) {
 if (previousBlock.index + 1 != block.index)
    return false;
    
 if (block.previousHash == null  ||
        block.previousHash != previousBlock.hash)
    return false;
    
 if (block.hash == null ||
        calculateHash(block) != block.hash)
    return false;
    
 return true;
}

Blockchain.prototype.isBlockchainValid = function() {
 if (!this.isFirstBlockValid())
    return false;
    
 for (var i = 1; i < this.blocks.length; i++) {
    var block = this.blocks[i];
    var previousBlock = this.blocks[i - 1];
    
    if (!this.isValidBlock(block, previousBlock))
       return false;
 }
 
 return true;
}

Blockchain.prototype.display = function() {
 for (var i = 0; i < this.blocks.length; i++) {
    var block = this.blocks[i];
    var str = "Block #" + block.index + " [" +
              "previousHash: " + block.previousHash + ", " +
              "timestamp: " + block.timestamp + ", " +
              "data: " + block.data + ", " +
              "hash: " + block.hash + "]";
    console.log(str);
 }
}