# Hello World Smart Contract in Solidity

This guide will walk through creating and deploying a simple smart contract on Ethereum using Metamask (opens new window)), Solidity (opens new window), Hardhat (opens new window), and Alchemy (opens new window).

# Connect to the Ethereum network

There are many ways to make requests to the Ethereum chain. For simplicity, you'll use a free account on Alchemy, a blockchain developer platform and API that allows us to communicate with the Ethereum chain without having to run our own nodes. The platform also has developer tools for monitoring and analytics that you'll take advantage of in this tutorial to understand what’s going on under the hood in our smart contract deployment. If you don’t already have an Alchemy account, you can sign up for free here (opens new window).

# Create your app (and API key)

Once you’ve created an Alchemy account, you can generate an API key by creating an app. This will allow us to make requests to the Ethereum network. If you’re not familiar with testnets, check out this guide (opens new window).

Navigate to the “Create App” page in your Alchemy Dashboard by hovering over “Apps” in the nav bar and clicking “Create App”.

Name your app “Hello World”, offer a short description, select “Staging” for the Environment (used for your app bookkeeping), click "Ethereum" for the Chain, and choose Ethereum for your network.

Click “Create app” and that’s it! Your app should appear in the table below.

# Create an Ethereum account (address)

You need to create an Ethereum account to send and receive transactions on the Ethereum network. For this tutorial, you'll use Metamask, a virtual wallet in the browser used to manage your wallet address. If you want to understand more about how transactions on Ethereum work, check out this guide (opens new window) by the Ethereum foundation. You can download and create a Metamask account for free here (opens new window). When you are creating an account, or if you already have an account, make sure to switch over to the “Ropsten Test Network”.

To get your customer Ethereum RPC URL from Alchemy, go to your "Hello World" app in your Alchemy dashboard and click "View Key" in the top right corner. Then, go ahead and copy your Alchemy HTTP API key.

You can download and create a Metamask account for free here (opens new window).

# Add ether from a faucet

In order to deploy the smart contract to the test network, you'll need testnet ETH. To get ETH, you can go to the Ropsten faucet (opens new window) and enter your Ropsten account address, then click “Send Ropsten Eth.” It may take some time to receive your testnet ETH due to network traffic.

# Check your Balance

To double-check our balance is there, let’s make an eth_getBalance (opens new window) request using Alchemy’s composer tool (opens new window). Select "Ethereum" as the chain, "Ropsten Test Network" as the network, "eth_getBalance" as the method, and input your address. This will return the amount of testnet ETH in your wallet. Check out this video (opens new window) for instructions on how to use the composer tool.

After you input your Metamask account address and click “Send Request”, you should see a response that looks like this:

{ "jsonrpc": "2.0", "id": 0, "result": "0xde0b6b3a7640000" }

This result is in Wei and not ETH

Wei is used as the smallest denomination of Ether. The conversion from Wei to ETH is: 1 ETH = 10^18 wei. So if we convert 0xde0b6b3a7640000 to decimal we get 1*10^18 which equals 1 ETH.

# Initialize your project

Start by creating a folder for your project:

mkdir hello-world
cd hello-world

You will create a new Node.js project for your smart contract.

If you don’t already have npm installed, follow these instructions (opens new window) (you'll also need Node.js so download that too).

Initialize a new Node.js project with:

npm init # (or npm init --yes)

It doesn’t really matter how you answer the installation questions, here is how we did it for reference:

package name: (hello-world)
version: (1.0.0)
description: hello world smart contract
entry point: (index.js)
test command:
git repository:
keywords:
author:
license: (ISC)

About to write to /Users/.../.../.../hello-world/package.json:

{   
   "name": "hello-world",
   "version": "1.0.0",
   "description": "hello world smart contract",
   "main": "index.js",
   "scripts": {
      "test": "echo \"Error: no test specified\" && exit 1"
   },
   "author": "",
   "license": "ISC"
}

Approve the package.json and your project is ready to go.

# Download Hardhat (opens new window)

Hardhat is a development environment to compile, deploy, test, and debug your Ethereum software. It helps developers when building smart contracts and dApps locally before deploying to the live chain.

Inside our hello-world project run:

npm install --save-dev hardhat

Check out this page for more details on installation instructions (opens new window).

# Create a Hardhat project

Inside the hello-world project folder, run:

npx hardhat

You should then see a welcome message and option to select what you want to do. Select “create an empty hardhat.config.js”:

888    888                      888 888               888
888    888                      888 888               888
888    888                      888 888               888
8888888888  8888b.  888d888 .d88888 88888b.   8888b.  888888
888    888     "88b 888P"  d88" 888 888 "88b     "88b 888
888    888 .d888888 888    888  888 888  888 .d888888 888
888    888 888  888 888    Y88b 888 888  888 888  888 Y88b.
888    888 "Y888888 888     "Y88888 888  888 "Y888888  "Y888

👷 Welcome to Hardhat v2.0.11 👷‍

What do you want to do? …
Create a sample project
❯ Create an empty hardhat.config.js
Quit

This will generate a hardhat.config.js file for us, which is where you'll specify all of the set up for our project (on step 13).

# Add project folders

To keep our project organized you'll create two new folders. Navigate to the root directory of your hello-world project in your command line and type:

mkdir contracts
mkdir scripts

contracts/ is where you'll keep our hello world smart contract code file
scripts/ is where you'll keep scripts to deploy and interact with our contract

# Write the contract

Open the "hello-world" project in your favorite editor. Smart contracts are written in a language called Solidity which is what you will use to write your "HelloWorld.sol" smart contract.‌

Navigate to the “contracts” folder and create a new file called HelloWorld.sol
Below is a sample Hello World smart contract from the Ethereum Foundation (opens new window) that you will be using for this tutorial. Copy and paste in the contents below into your HelloWorld.sol file, and be sure to read the comments to understand what this contract does:

// SPDX-License-Identifier: None

// Specifies the version of Solidity, using semantic versioning.
// Learn more: https://solidity.readthedocs.io/en/v0.5.10/layout-of-source-files.html#pragma
pragma solidity >=0.8.9;

// Defines a contract named `HelloWorld`.
// A contract is a collection of functions and data (its state). Once deployed, a contract resides at a specific address on the Ethereum blockchain. Learn more: https://solidity.readthedocs.io/en/v0.5.10/structure-of-a-contract.html
contract HelloWorld {

   //Emitted when update function is called
   //Smart contract events are a way for your contract to communicate that something happened on the blockchain to your app front-end, which can be 'listening' for certain events and take action when they happen.
   event UpdatedMessages(string oldStr, string newStr);

   // Declares a state variable `message` of type `string`.
   // State variables are variables whose values are permanently stored in contract storage. The keyword `public` makes variables accessible from outside a contract and creates a function that other contracts or clients can call to access the value.
   string public message;

   // Similar to many class-based object-oriented languages, a constructor is a special function that is only executed upon contract creation.
   // Constructors are used to initialize the contract's data. Learn more:https://solidity.readthedocs.io/en/v0.5.10/contracts.html#constructors
   constructor(string memory initMessage) {

      // Accepts a string argument `initMessage` and sets the value into the contract's `message` storage variable).
      message = initMessage;
   }

   // A public function that accepts a string argument and updates the `message` storage variable.
   function update(string memory newMessage) public {
      string memory oldMsg = message;
      message = newMessage;
      emit UpdatedMessages(oldMsg, newMessage);
   }
}

This is a simple smart contract that stores a message upon creation and can be updated by calling the update function.

# Connect Metamask & Alchemy to your project

You have created a Metamask wallet, Alchemy account, and written our smart contract, now it’s time to connect the three.

Every transaction sent from your virtual wallet requires a signature using your unique private key. To provide our program with this permission, you can safely store our private key (and Alchemy API key) in an environment file.

To learn more about sending transactions, check out this tutorial (opens new window) on sending transactions using web3.

First, install the dotenv package in your project directory:

npm install dotenv --save

Then, create a .env file in the root directory of our project, and add your Metamask private key and HTTP Alchemy API URL to it.

Your environment file must be named .env or it won't be recognized as an environment file.

Do not name it process.env or .env-custom or anything else.

WARNING: If you are using version control system like git to manage your project, please DO NOT track the .env file. Add .env to your .gitignore file so that you don't accidentally publish your secrets to the world

Follow these instructions (opens new window) to export your private key
To get your Alchemy HTTP API Key (RPC URL), go to your "Hello World" app in your Alchemy dashboard and click "View Key" in the top right corner. Then go ahead and copy your Alchemy HTTP API key!

Your .env should look like this:

API_URL = "https://eth-goerli.alchemyapi.io/v2/your-api-key"
PRIVATE_KEY = "your-metamask-private-key"

To actually connect these to our code, you'll reference these variables in our hardhat.config.js file on step 13.

# Install Ethers.js

Ethers.js is a library that makes it easier to interact and make requests to Ethereum by wrapping standard JSON-RPC methods (opens new window) with more user-friendly methods.

Hardhat makes it super easy to integrate Plugins (opens new window) for additional tooling and extended functionality. You'll be taking advantage of the Ethers plugin (opens new window) for contract deployment (Ethers.js (opens new window) has some super clean contract deployment methods).

In your project directory type:

npm install --save-dev @nomiclabs/hardhat-ethers "ethers@^5.0.0"

You'll also require ethers in our hardhat.config.js in the next step.

# Update hardhat.config.js

You have added several dependencies and plugins so far, now, you need to update hardhat.config.js so that our project knows about all of them.

Update your hardhat.config.js to look like this:

/**
* @type import('hardhat/config').HardhatUserConfig
*/

require('dotenv').config();
require("@nomiclabs/hardhat-ethers");

const { API_URL, PRIVATE_KEY } = process.env;

module.exports = {
   solidity: "0.8.9",
   defaultNetwork: "goerli",
   networks: {
      hardhat: {},
      goerli: {
         url: API_URL,
         accounts: [`0x${PRIVATE_KEY}`]
      }
   },
}

# Compile our contract

To make sure everything is working so far, let’s compile our contract. The compile task is one of the built-in hardhat tasks.

From the command line run:

npx hardhat compile

You might get a warning about SPDX license identifier not provided in source file , but no need to worry about that — hopefully everything else looks good! If not, you can always message in the Alchemy discord (opens new window).

# Write our deploy script

Now that our contract is written and our configuration file is good to go, it’s time to write our contract deploy script.

Navigate to the scripts/ folder and create a new file called deploy.js, adding the following contents to it:

async function main() {
   const HelloWorld = await ethers.getContractFactory("HelloWorld");

   // Start deployment, returning a promise that resolves to a contract object
   const hello_world = await HelloWorld.deploy("Hello World!");   
   console.log("Contract deployed to address:", hello_world.address);
}

main()
  .then(() => process.exit(0))
  .catch(error => {
    console.error(error);
    process.exit(1);
  });

const HelloWorld = await ethers.getContractFactory("HelloWorld");

A ContractFactory in ethers.js is an abstraction used to deploy new smart contracts, so HelloWorld here is a factory (opens new window) for instances of our hello world contract. When using the hardhat-ethers plugin ContractFactory and Contract, instances are connected to the first signer (owner) by default.

const hello_world = await HelloWorld.deploy();

Calling deploy() on a ContractFactory will start the deployment, and return a Promise that resolves to a Contract object. This is the object that has a method for each of our smart contract functions.

# Deploy the contract

You're ready to deploy our smart contract! Navigate to the command line and run:

npx hardhat run scripts/deploy.js --network goerli

You should then see something like:

Contract deployed to address: 0x3d94af870ED272Cd5370e4135F9B2Bd0e311d65D

Please copy and paste this address to save it somewhere, as you will be using this address for later tutorials, so you don't want to lose it.

If you go to the Ethereum block explorer (Etherscan) (opens new window) and search for your contract address, you should be able to see that it has been deployed successfully.

The From address should match your Metamask account address and the To address will say “Contract Creation”. But if you click into the transaction, you'll see our contract address in the To field:

Congrats! You just deployed a smart contract to the Ethereum blockchain.

To understand what’s going on under the hood, let’s navigate to the Explorer tab in our Alchemy dashboard (opens new window). If you have multiple Alchemy apps make sure to filter by app and select “Hello World”.

Here, you’ll see a handful of JSON-RPC calls that Hardhat/Ethers made under the hood for us when you called the .deploy() function. Two important ones to call out here are eth_sendRawTransaction (opens new window), which is the request to actually write our contract onto the Ethereum chain, and eth_getTransactionByHash (opens new window) which is a request to read information about our transaction given the hash (a typical pattern when sending transactions).

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