Create Your Own Cryptocurrency with JavaScript

Cryptocurrency is a decentralized form of digital currency that operates independently of a central bank or government. Cryptocurrency development relies on blockchain technology, which is a distributed ledger that records all transactions across multiple computers or nodes. In this blog post, we will simulate a blockchain with javascript code in which users can have wallets that contain public and private keys.

Cryptocurrency Development with JavaScript

We will simulate a blockchain using JavaScript code, where users can possess wallets containing public and private keys. Within this simulation, users have the ability to initiate transactions that are subsequently incorporated into blocks, eventually forming a complete blockchain structure.

For the implementation, we will have 4 classes - Transaction, Block, Wallet, and Chain.

Transaction Class

This class simulates the transaction on a blockchain

Constructor:

• The constructor method is called when a new instance of the Transaction class is created.
• It takes three parameters: amount, senderAddress, and receiverAddress.
• These parameters represent the amount of the transaction and the addresses of the sender and receiver, respectively.
• Inside the constructor, the values are assigned to the corresponding properties of the transaction object.

toString() method:

• This method converts the transaction object to a string representation.
• It returns a JSON string representation of the transaction object using JSON.stringify(this).
• The ‘this’ keyword refers to the current transaction object.

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Block Class

This class simulates the blocks on the blockchain.

Constructor:

• The constructor method is called when a new instance of the Block class is created.
• It takes three parameters: previousHash, transaction, and timestamp.
• previousHash represents the hash of the previous block in the chain.
• transaction is the transaction associated with the current block.
• timestamp is an optional parameter representing the timestamp of when the block was created. If not provided, the current timestamp (obtained using Date.now()) is used.
• Inside the constructor, the values are assigned to the corresponding properties of the block object.

getHash() method:

• This method calculates and returns the hash of the block.
• It converts the block object to a JSON string representation using JSON.stringify(this).
• It then uses the SHA-256 algorithm from the crypto module to compute the hash of the JSON string.
• The resulting hash is returned as a hexadecimal string.

toString() method:

• This method converts the block object to a string representation.
• It returns a JSON string representation of the block object using JSON.stringify(this).
• The ‘this’ keyword refers to the current block object.

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Wallet Class

This class simulates the wallet on the blockchain.

Constructor:

• The constructor method is called when a new instance of the Wallet class is created.
• Inside the constructor, a key pair is generated using the crypto.generateKeyPairSync() function from the crypto module.
• The generateKeyPairSync() function generates a public-private key pair using the RSA encryption algorithm.
• The key pair is then stored in the privateKey and publicKey properties of the wallet object.

send(amount, receiverAddress) method:

• This method facilitates a transaction by creating a new Transaction object, signing it with the sender's private key, and inserting a new block into the blockchain.
• It takes two parameters: amount (the amount to be sent in the transaction) and receiverAddress (the address of the recipient).
• Inside the method, a new Transaction object is created using the provided amount, the wallet's publicKey as the sender's address, and the receiverAddress as the recipient's address.
• The crypto.createSign() function is used to create a sign object with the SHA-256 hashing algorithm.
• The update() method of the sign object is called with the transaction converted to a string using transaction.toString().
• The sign() method is then called on the sign object, passing the wallet's privateKey to sign the transaction.
• The resulting signature is passed along with the transaction and the wallet's publicKey to the insertBlock() method of the Chain class, adding a new block to the blockchain.

Chain Class

This class simulates the blockchain itself.

Constructor:

• The constructor method is called when a new instance of the Chain class is created.
• Inside the constructor, the initial state of the blockchain is set by creating a genesis block.
• The genesis block is created using an empty string as the previous hash and a default transaction with zero amount and arbitrary sender and receiver addresses.
• The genesis block is then stored as the first block in the chain array.

getPreviousBlockHash() method:

• This method returns the hash of the previous block in the chain.
• It retrieves the last block in the chain array using this.chain[this.chain.length - 1].
• The getHash() method of the block object is called to obtain its hash.

insertBlock(transaction, senderAddress, sig) method:

• This method inserts a new block into the blockchain after verifying the integrity and authenticity of the provided transaction.
• It takes three parameters: transaction (the transaction to be included in the block), senderAddress (the address of the transaction sender), and sig (the signature of the transaction signed by the sender).
• Inside the method, a crypto.createVerify() object is created with the SHA-256 hashing algorithm to perform the verification.
• The update() method of the verify object is called with the string representation of the transaction obtained using transaction.toString().
• The verify() method is then called on the verify object, passing the senderAddress and the sig to verify the signature.
• If the signature is valid, a new block is created using the getPreviousBlockHash() method to retrieve the previous block's hash.
• The new block is added to the chain array using this.chain.push(block).

getBalance(address) method:

• This method calculates and returns the balance of a user based on their address.
• It takes one parameter: address (the address of the user).
• Inside the method, a variable named balance is initialized to zero.
• The method iterates over each block in the chain array using forEach().
• For each block, it checks if the senderAddress of the block's transaction matches the given address. If true, it subtracts the transaction amount from the balance.
• It also checks if the receiverAddress of the block's transaction matches the given address. If true, it adds the transaction amount to the balance.
• Finally, the calculated balance is returned.

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