June 26, 2021

How to create and deploy a smart contract with Hardhat

Overview

Ethereum development environments like Truffle and Hardhat make it easier to work with smart contracts and Ethereum nodes. They provide a set of tools to seamlessly write, test, and deploy smart contracts. In this guide, we’ll create a hello world smart contract and deploy it using hardhat via QuickNode.

Prerequisites: 
  • Node.js installed on your system
  • CLI/Terminal
  • Text Editor

What is Hardhat?

Hardhat is a development environment that helps developers compile, deploy, test, and debug their Ethereum applications. It has some of the cleanest, most detailed documentation. Hardhat also provides console.log() functionality, similar to javascript for debugging purposes. Hardhat also has many plugins, which further increases its functionality.

Installing hardhat and other dependencies

We’ll install hardhat using npm, which comes with node.js

First, create a new project directory and cd into it. Feel free to use your own names here instead:
mkdir HardhatTutorial
cd HardhatTutorial

Open terminal/cmd in your project directory and type the following.

npm install -d hardhat

Now that we have hardhat installed let’s start a new hardhat project. We’ll use npx to do so. Npx helps process node.js executables. 

npx hardhat

You’ll be greeted with a CLI hardhat interface. Select the second option, "Create an empty hardhat.config.js", and press enter.


Now, let’s install other dependencies required to work with hardhat.

npm install --save-dev @nomiclabs/hardhat-ethers ethers @nomiclabs/hardhat-waffle ethereum-waffle chai

We need these dependencies to write automated tests for contracts.

The most common issue while installing packages with npm can be an internal failure with `node-gyp`. You can follow node-gyp installation instructions here.

Note: You will need to have your python version match one of the compatible versions listed in the instructions above if you encounter the node-gyp issue. 

Another common issue is a stale cache. Clear your npm cache by simply typing the below into your terminal:

npm cache clean

Now, let’s get a private key for our wallet, some test ETH for gas, and an Ethereum node in place; all of which we'll need to deploy our smart contract.

Getting the private key

We’ll need an Ethereum wallet/address to sign the smart contract deployment transaction. To set up the wallet, get its private key and add it to the config file of hardhat.

You can follow QuikNode guides to generate a private key and an Ethereum address in JavaScript, Ruby, Python, Go, PHP.

You can also get a private key from your MetaMask wallet. To do so, open your MetaMask browser plugin, select Ropsten network and click on the three dots below the favicon.


Now, click on “Account details”


Then click on “Export Private Key”


Enter your password and click on confirm. It’ll display your private key (similar to the above image).


Copy and save the private key; we’ll need it in the later steps.

It is recommended to store sensitive information like private keys in a .env file and get it into the config file using env variable or make a new secondary MetaMask wallet for development purpose.

Getting testnet ETH

We’ll deploy our contract on the Ropsten testnet. To get started, we will need some test ETH in our MetaMask wallet, which we saw in the last step. You can get it by going to the Ropsten faucet. You'll need to select “Ropsten Test Network” on your MetaMask wallet, copy-paste the wallet address into the text field in the faucet, and then click “Send me test Ether”.

Booting an Ethereum node

To deploy our contract on Ethereum’s Ropsten blockchain we will need access to an Ethereum Ropsten node. For that, we could use pretty much any Ethereum client such as Geth or OpenEthereum (fka Parity). Since that is a bit too involved for deploying a single contract, we'll just grab a free trial Ropsten endpoint from QuickNode to make this easy. After you've created your free ethereum endpoint, copy your HTTP Provider endpoint.
 

You'll need this later, so copy and save it.

Setting up the config file

Open the hardhat.config.js file and paste the following into it:

require("@nomiclabs/hardhat-waffle");

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

const Private_Key = "ADD_YOUR_PRIVATE_KEY_HERE"

module.exports = {
  solidity: "0.7.3",
  networks: {
  	ropsten: {
  		url: `ADD_YOUR_QUICKNODE_URL_HERE`,
  		accounts: [`0x${Private_Key}`]
  	}
  }
};

Replace ADD_YOUR_PRIVATE_KEY_HERE with the private key we obtained in the previous step and replace ADD_YOUR_QUICKNODE_URL_HERE with the HTTP node URL we obtained in the previous step.

Explanation of the code above:

Line 1: Importing the hardhat-waffle package.

Line 7: Storing our private key in the Private_Key variable.

Line 9-17: Mentioning Solidity version, network type, node URL, and accounts where we are supplying the private key and adding 0x as a prefix.

Save the file.

Creating contract

Now, for our contract, create a new directory "contracts" and place a new file "helloworld.sol" inside.

Copy-paste the following into your solidity script file:

// SPDX-License-Identifier: MIT
pragma solidity ^0.7.3;

contract HelloWorld {

    string saySomething;

    constructor() {
        saySomething = "Hello World!";
    }

    function speak() public view returns(string memory) {
        return saySomething;
    }
}

Explanation of the code above:

Line 1: Specifying SPDX license type, which is an addition after Solidity ^0.6.8. 

Whenever the source code of a smart contract is made available to the public, these licenses can help  resolve/avoid copyright issues. If you do not wish to specify any license type, you can use a special license UNLICENSED or simply skip the whole comment (it won’t result in an error, just a warning).

Line 2: Declaring the solidity version.
 
Line 4: Starting our contract named HelloWorld.
 
Line 6: Creating a variable saySomething of type string.

Line 8-10: Initiating the constructor and storing the string “Hello World!” in the saySomething variable.

Line 12-14: Creating a function called speak of type public, which will return the string stored in the saySomething variable.

Save the file and compile the contract using the following hardhat command.

npx hardhat compile

If your contract compiles successfully, it will give an output like this:

Deploying contract

Now to deploy our contract, let’s create a deploy.js file in a new directory named scripts.

Copy-paste the following into your deploy.js file:

async function main() {

	const [deployer] = await ethers.getSigners();

	console.log(
	"Deploying contracts with the account:",
	deployer.address
	);

	console.log("Account balance:", (await deployer.getBalance()).toString());

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

	console.log("Contract deployed at:", contract.address);
}

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

Explanation of the code above.

Line 1: Starting an async function.

Line 3: Getting the Ethereum address to sign the transaction and storing it in the deployer address. 

Line 5-8: Printing the Ethereum address along with a string to the console.

Line 10: Printing the balance of the Ethereum address in wei to console. Wei is the smallest unit of ether, one Wei = 10^−18 ETH.

Line 12: Calling the ethers.js method ContractFactory. This will look for the "HelloWorld.sol" file, and return an instance that we can use ContractFactory methods on.

Line 13: Calling deploy on ContractFactory to deploy the contract. 

Line 15: Printing the address of the deployed contract to the console.

Line 18: Invoking the function "main".

Line 19-22: Checking for error, printing if any error, and exiting the process.

Save the file and run the following to deploy the contract.

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

Note: The network flag can be skipped if deploying to the mainnet.

On the successful deployment of the contract you will see an output containing the deployed contract’s address.


We can verify the deployment by copying and pasting the deployed contract’s address in Ropsten Etherscan’s search bar. This will display information about the deployed contract.

Conclusion

Here we saw how to work with hardhat. Using hardhat, you can write tests for your contracts and debug them without sweating too much. Refer to hardhat’s official documentation for more information.

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