D-Ledger: A Decentralized Application on the Internet Computer

Table of Contents

• Introduction
• Theory Notes
  • Internet Computer
  • DFX
• Features and Functionality
• Implementation
  • Backend Code
  • Frontend Code
• Running the Project Locally

Introduction

D-Ledger is a decentralized application (dApp) created to learn and demonstrate the capabilities of the Internet Computer (IC) blockchain. This application simulates a simple banking system where users can top-up, withdraw, and check their balance.

Theory Notes

Internet Computer

The Internet Computer is a blockchain that runs at web speed with unbounded capacity. It aims to extend the functionality of the public internet so that it can host backend software, transforming it into a global compute platform. Key features include:

• Canisters: Smart contracts on the Internet Computer that combine code and state.
• Cycles: The fuel that powers computation in the Internet Computer.
• Motoko: A programming language designed for the Internet Computer.

DFX

DFX is the command-line tool used to manage, deploy, and interact with canisters on the Internet Computer. Key commands include:

• dfx start: Starts the local replica.
• dfx new <project-name>: Creates a new project.
• dfx deploy: Deploys the canisters.
• dfx canister call <canister-name> <method-name>: Calls a method on a canister.

To learn more before you start working with dbank2, see the following documentation available online:

• Quick Start
• SDK Developer Tools
• Motoko Programming Language Guide
• Motoko Language Quick Reference

Features and Functionality

• Top-Up: Allows users to add funds to their account.
• Withdraw: Enables users to withdraw funds from their account, ensuring the balance does not go negative.
• Check Balance: Users can query their current balance at any time.
• Compound Interest: The balance compounds over time, simulating interest accrual.

Implementation

Backend Code

The backend canister is written in Motoko and manages the core banking operations: topping up, withdrawing, checking the balance, and compounding interest.

Frontend Code

The frontend is a simple HTML page with a form for user interactions and JavaScript for handling user input and communicating with the backend.

Running the Project Locally

If you want to test your project locally, you can use the following commands:

• Starts the replica, running in the background

dfx start --background

• Deploys your canisters to the replica and generates your candid interface

dfx deploy

• If you have made changes to your backend canister, you can generate a new candid interface with

npm run generate

at any time. This is recommended before starting the frontend development server, and will be run automatically any time you run dfx deploy

• Start a development server with

npm start

Which will start a server at http://localhost:8080, proxying API requests to the replica at port 4943.

npm start

Which will start a server at http://localhost:8080, proxying API requests to the replica at port 4943.