aa-oracle-zkevm

A reference example of a stablecoin based on an API3 ETH/USD price feed on Polygon zkEVM Testnet.

Blockchain: Polygon zkEVM Testnet

Polygon zkEVM Documentation

Network	Public RPC URL	ChainID	Block Explorer URL	Verification API Key
Polygon zkEVM Testnet	https://rpc.public.zkevm-test.net	1442	https://testnet-zkevm.polygonscan.com	https://zkevm.polygonscan.com/myapikey

Data feed: API3 ETH-USD

Read a dAPI documentation

ETH-USD dAPI: https://market.api3.org/dapis/polygon-zkevm-testnet/ETH-USD

Project logic

TokenSwap checks the ETH-USD price from the API3 data feed on Polygon zkEVM Testnet and allows users to deposit ETH (collateral) to get (N ETH * ETH-USD price) / (1e18) STA stable tokens. STA tokens can be burned to reclaim for ETH based on the current ETH-USD price at any time.

• TokenSwap Contract: https://testnet-zkevm.polygonscan.com/address/0x1fba51630d9557710778e827d786db624ee3c4e1

• TokenSwap Stable (STA) Token transfers: https://testnet-zkevm.polygonscan.com/token/0x1fba51630d9557710778e827d786db624ee3c4e1

• API3 ETH-USD dAPI Polygon zkEVM Testnet data feed: https://market.api3.org/dapis/polygon-zkevm-testnet/ETH-USD

Examples

ETH	ETH-USD price (uint256)	ETH-USD price $	STA tokens	tx
1	1500000000000000000000	$1,500	1500	example
1	2000000000000000000000	$2,000	2000	example
.01	1893000000000000000000	$1,893	18.93	https://testnet-zkevm.polygonscan.com/token/0x1fba51630d9557710778e827d786db624ee3c4e1
1	1893000000000000000000	$1,893	1893	https://testnet-zkevm.polygonscan.com/tx/0xd4a309ad49a805a100fa18b3cdd0f45a1b4cd0da2794771b5420d000443a6bf5

Getting started

0. Wallet setup: Create a Metamask wallet, add the Polygon zkEVM testnet network to your Metamask networks, and get Polygon zkEVM testnet ETH

• Visit the Polygon zkEVM Testnet blockchain explorer page
• Scroll down to the bottom
• Click the “🦊 Add zkEVM Network” button
• Open Metamask and switch your Metamask network to "zkEVM testnet"
• Use the Polygon Faucet to add .02 Polygon zkEVM testnet ETH to your account

Backend setup

1. Enter backend directory and install dependencies:

cd backend
yarn

2. Create a .env file by copying the .env.example file:

cp .env.example .env

Update the .env file with your PRIVATE_KEY from Metamask and your ZKEVM_POLYGONSCAN_API_KEY from Polygonscan: https://zkevm.polygonscan.com/myapikey

3. Compile contracts:

npx hardhat compile

4. Deploy contracts to Polygon zkEVM Testnet

npx hardhat run scripts/deploy.ts --network polygonZKEVMTestnet

Note: The hardhat config file sets up artifacts to be output to the frontend/artifacts directory. You can find the ABI in frontend/artifacts/contracts/TokenSwap.sol/TokenExchange.json

Example deployed contract: https://testnet-zkevm.polygonscan.com/address/0x1fba51630d9557710778e827d786db624ee3c4e1

5. Verify contracts on Polygon zkEVM Testnet

Copy the contract address from the output of the previous command and run:

npx hardhat verify --network polygonZKEVMTestnet <your-contract-address>

Check out your verified contract on Polygonscan using the link output by the verification command.

Example verified contract: https://testnet-zkevm.polygonscan.com/address/0x1fba51630d9557710778e827d786db624ee3c4e1#code

6. Use the verified contract on Polygonscan to setProxyAddress

The proxy contract address for the API3 ETH-USD on the Polygon zkEVM Testnet is 0x26690F9f17FdC26D419371315bc17950a0FC90eD

Use the link from the verification command output to view your contract on Polygonscan. Click the "Write Contract" tab. Click "Connect to Web3" and use Metamask to sign in with the account you used to deploy the contract. After signing in, select the setProxyAddress function. Enter the proxy contract address for the dApi and click "Write." Confirm the tx in your Metamask wallet.

Example setProxyAddress tx: https://testnet-zkevm.polygonscan.com/tx/0x432b9039a1b99b04798dac319fdf175895064263e9660bd9d6e6ed1ca35689ec

Frontend setup

1. Enter frontend directory and install dependencies:

cd frontend
yarn

2. Create a .env.local file by copying the .env.example file:

cp .env.example .env.local

3. Get a Wallet Connect Project ID

• Log in to the Wallet Connect dashboard and create a new named project
• Update the NEXT_PUBLIC_WALLET_CONNECT_PROJECT_NAME variable in the .env.local file with your new Wallet Connect Project Name, to match the name you gave your project in the Wallet Connect dashboard
• Update the NEXT_PUBLIC_WALLET_CONNECT_PROJECT_ID variable in the .env.local file with your new Wallet Connect Project ID from the dashboard

4. Get an Alchemy Key

• Sign in to the Alchemy dashboard
• Create app with a name of your choice. Select "Polygon zkEVM" for chain and "Polygon zkEVM Testnet" for network
• Select "View key" for the project you just created
• Update the NEXT_PUBLIC_ALCHEMY_KEY variable in the .env.local file with your new Alchemy Key

5. Add your private key

• Update the NEXT_PUBLIC_PRIVATE_KEY env variable with your private key from Metamask

6. Start the project by running the development server:

yarn run dev