A hash function computes a string or digest from selected input values. The result summarizes an object's state and supports fast lookup and data-integrity checks, but a simple algorithm can produce collisions. section 2.1.2 section 4.3.2
Hashing serves several related purposes:
- Hash transaction values into identifiers, such as a blockchain transactionId. section 2.1.2
- Link blockchain blocks by including the previous block's cryptographically secure hash in the next block. section 1.6
- Separate data assembly from digest computation so the hashing algorithm can be replaced without rewriting surrounding code. section 4.3.2
Hashing a transaction
A transaction object can define calculateHash by joining selected values such as sender and recipient, processing each character, and returning a numeric digest. A derived moneyTransaction inherits that method while adding funds. In a blockchain, changing one transaction property changes its hash and invalidates the subsequent chain. section 2.1.2 section 1.6
Listing 2.4 Creating hashTransaction with basic hashing calculation
const hashTransaction = Object.create(transaction);
hashTransaction.calculateHash = function calculateHash() { #1
const data = [this.sender, this.recipient].join(''); #2
let hash = 0, i = 0;
while (i < data.length) {
hash = ((hash << 5) - hash + data.charCodeAt(i++)) << 0;
}
return hash**2; #3
}
hashTransaction.calculateHash(); // 237572532174000400
Shows a basic JavaScript hash implementation that selects object values, iterates through their characters, and returns a digest. section 2.1.2
