Vending Machine dApp

This is a decentralized application (dApp) built to explore how smart contracts talk to a web frontend. I built this to understand the "bridge" that connects blockchain logic to a user-friendly interface.

Project Goals

The main purpose of this project was to master three core concepts:

1. Understanding ABIs: Learning that an ABI (Application Binary Interface) is the essential "instruction manual." It tells our JavaScript exactly which functions exist on the blockchain and what data they need.
2. Working with ethers.js: Using this library as the engine to connect to MetaMask, sign transactions, and handle the math for sending ETH.
3. Real-World Interaction: Moving beyond just reading data to actually sending "payable" transactions (sending 2 ETH per coke) to the network.

How It's Built

• The Smart Contract: This is an ABC project. The Vending Machine logic was sourced from the ABC official Gitbook. It manages inventory and handles the purchase math.
• The Frontend: A clean, simple HTML/JS setup that doesn't require complex frameworks, making it easier to see the underlying logic.
• The Connection: We use ethers.js to create a "Contract Object" in the browser, which lets us trigger the purchase function with a button click.

Smart Contract

The VendingMachine contract manages a coke inventory:

• getVendingMachineBalance() — returns current stock
• restock(uint amount) — owner-only, adds to inventory
• purchase(uint amount) — payable, costs 0.00001 ETH per unit

Deployed on Sepolia at 0xB266590c076742C52D790786D16aAED5F1665685.

Key Takeaways

• The Bridge: Without the ABI, the website is "blind" to the contract.
• Wallet Integration: Learned how to request account access and use a "Signer" to authorize blockchain actions.
• Wei vs ETH: Gained experience using utility functions to convert human-readable ETH into the "Wei" units that the blockchain requires.

Screenshot