Simple Blockchain Simulation in JavaScript

A minimal blockchain simulation to demonstrate key blockchain concepts such as block linking, hashing, validation, and proof-of-work.

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Getting Started

Prerequisites

• Node.js (v18+ recommended)
• npm

Installation

npm install

Run the Simulation

npm start

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Features

• Add dummy transactions before mining
• Mine blocks with proof-of-work
• Print the blockchain
• Tamper with the blockchain and detect it using validation
• Modular code with Block and Blockchain classes

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Project Structure

.
├── blockchain.js        # Block and Blockchain class definitions
├── index.js             # Driver code to run the simulation
├── package.json         # Node.js project metadata and scripts
└── README.md            # Project overview and instructions

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Evaluation Criteria

Functionality

• ✅ Blockchain with Linked Blocks:
  Each block contains a reference (previousHash) to the hash of the previous block, ensuring a linked structure that mimics real-world blockchains.

• ✅ Validation Method:
  The isChainValid() method verifies:

  • The integrity of each block’s hash.
  • The correctness of the block linkage via previousHash.
    Tampering with any block's data will break the chain’s integrity and be detected.

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Code Quality

• ✅ Well-Structured and Modular:
  The project uses object-oriented design with:

  • A Block class (handles hashing and mining logic).
  • A Blockchain class (manages the chain, validation, and transactions).

• ✅ Readable Code:
  Variable names are descriptive, and the logic follows a clean, intuitive flow.

• ⚠️ Comments:
  While the code is mostly self-explanatory, basic inline comments can be added to enhance understanding for newer developers.

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Optional Bonus Features

• ✅ Proof-of-Work (PoW):
  Implemented in the mineBlock() method using a configurable difficulty level. Blocks are mined only when their hash starts with a specific number of leading zeroes (e.g., "000" for difficulty 3), simulating computational effort.

• ✅ Dynamic Transactions:
  Transactions are added using createTransaction() and grouped into blocks during minePendingTransactions() — allowing multiple transactions per block before mining.

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Docker (Optional)

Build and Run with Docker

docker build -t simple-blockchain .
docker run simple-blockchain