HelloWorld.md

HelloWorld Contract

The HelloWorld contract is the classic starting point for BitGov. It stores a single greeting string on-chain and exposes functions to read and update it.

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Contract overview

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.28;

contract HelloWorld {
    string private _message;

    event MessageChanged(string newMessage);

    constructor(string memory initialMessage) {
        _message = initialMessage;
    }

    function getMessage() external view returns (string memory) {
        return _message;
    }

    function setMessage(string memory newMessage) external {
        _message = newMessage;
        emit MessageChanged(newMessage);
    }
}

Concept	Meaning
pragma solidity ^0.8.28	Specifies the minimum compiler version
string private _message	A state variable — stored permanently on-chain
constructor(...)	Runs once at deployment
external view	Read-only function; no gas cost when called off-chain
emit MessageChanged(...)	Fires an event — cheap, indexable log entry on the blockchain

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Deploy

npx hardhat ignition deploy ignition/modules/intro/HelloWorld.ts --network localhost

The deployment module passes "Hello, World!" as the initial message. Note the address printed at the end of the output — you will need it for the console session below.

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Interact via Hardhat console

1 — Start a local node (first terminal)

npx hardhat node

2 — Deploy (second terminal)

npx hardhat ignition deploy ignition/modules/intro/HelloWorld.ts --network localhost
# Deployed HelloWorldModule#HelloWorld at 0x5FbDB2315678afecb367f032d93F642f64180aa3

3 — Open the Hardhat console

npx hardhat console --network localhost

4 — Get ethers from the network connection

In Hardhat v3, ethers is accessed via the network global that the console provides.

const { ethers } = await network.connect();

5 — Attach to the deployed contract

const hw = await ethers.getContractAt("HelloWorld", "0x5FbDB2315678afecb367f032d93F642f64180aa3");

6 — Read the current message

await hw.getMessage();
// 'Hello, World!'

7 — Update the message

await hw.setMessage("Hello, BitGov!");
await hw.getMessage();
// 'Hello, BitGov!'