Polygon

 

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" }

NOTE

This result is in Wei, not ETH. Wei is used as the smallest denomination of Ether. The conversion from Wei to Ether is: 1 Ether = 10^18 Wei. So, if we convert “0xde0b6b3a7640000” to decimal, we get 1*10^18, which equals 1 ETH. This can be mapped to 1 MATIC based on denomination.

Step 6: Initialize your project

First, we’ll need to create a folder for our project. Navigate to your command line and type:

mkdir hello-worldcd hello-world

Now that we’re inside our project folder, we’ll use npm init to initialize the project. If you don’t already have npm installed, follow these instructions (we’ll also need Node.js so download that too!).

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 we’re good to go!

Step 7: Download Hardhat

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.

Step 8: Create Hardhat project

Inside our 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 v2.12.2 👷‍

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

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

Step 9: Add project folders

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

mkdir contractsmkdir scripts

• contracts/ is where we’ll keep our hello world smart contract code file

• scripts/ is where we’ll keep scripts to deploy and interact with our contract

Step 10: Write the contract

Open up the hello-world project in your favorite editor, such as VSCode. Smart contracts are written in a language called Solidity which is what we will use to write our HelloWorld.sol smart contract.‌

1. Navigate to the “contracts” folder and create a new file called HelloWorld.sol

2. Below is a sample Hello World smart contract from the Ethereum Foundation that we 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
   #pragmapragma 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 super simple smart contract that stores a message upon creation and can be updated by calling the update function.

   Step 11: Connect Metamask & Alchemy to your project

   We’ve 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, we can safely store our private key (and Alchemy API key) in an environment file.

   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.

   DANGER

   If you are using a version control system like git to manage your project, please DO NOT track the .env file. Add .env to your .gitignore file to avoid publishing secret data.

   • Follow these instructions to export your private key

   • To get your Alchemy HTTP API key (RPC URL), navigate to your “Hello World” app on your account’s dashboard and click “View Key” in the top right corner.

   Your .env should look like this:

   API_URL = "https://polygon-mumbai.g.alchemy.com/v2/your-api-key"PRIVATE_KEY = "your-metamask-private-key"

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

   Step 12: 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 with more user-friendly methods.

   Hardhat makes it easy to integrate plugins for additional tooling and extended functionality. We’ll be taking advantage of the Ethers plugin for contract deployment. Ethers.js has useful contract deployment methods.

   In your project directory type:

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

   We’ll also require ethers in our hardhat.config.js in the next step.

   Step 13: Update hardhat.config.js

   We’ve added several dependencies and plugins so far, now we 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: "polygon_mumbai",
      networks: {
         hardhat: {},
         polygon_mumbai: {
            url: API_URL,
            accounts: [`0x${PRIVATE_KEY}`]
         }
      },
   }

   Step 14: 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 the pllication might still be working fine. If not, you can always message in the Alchemy discord.

   Step 15: 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);
     });

   We’ve adopted the Hardhat team explanations to what each of these lines of code does from their Contracts tutorial here.

   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 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.

   Step 16: Deploy our contract

   Navigate to the command line and run:

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

   You should then see something like:

   Contract deployed to address: 0x3d94af870ED272Cd5370e4135F9B2Bd0e311d65D

   If we go to the Polygon Mumbai explorer and search for our contract address we 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 we click into the transaction, we’ll see our contract address in the To field:

Step 17: Verify the contract

Alchemy provides an explorer where you can find information about the methods deployed along with the smart contract, such as response time, HTTP status, error codes and others. It is a good environment to verify your contract and check whether the transactions went through.

Congratulations! You just deployed a smart contract to the Polygon chain.