How-to: Grant USDC Allowance to Permit2

import {
  createWalletClient,
  createPublicClient,
  http,
  custom,
  erc20Abi,
} from "viem";
import { sepolia } from "viem/chains";
import dotenv from "dotenv";

dotenv.config();

/**
 * Approves a specified amount of USDC for the Permit2 contract using
 * a custom wallet with an EIP-1193 provider (like MetaMask).
 *
 * This function sends an on-chain transaction to call the ERC-20 `approve`
 * method on the USDC contract, allowing the Permit2 contract to spend
 * the specified amount on behalf of the wallet.
 *
 * @async
 * @function approveUSDCWithEIP1193Wallet
 * @param {any} [provider] - EIP-1193 provider.
 * @returns {Promise<object>} The transaction hash and receipt.
 */
export async function approveUSDCWithEIP1193Wallet(provider) {
  const publicClient = createPublicClient({
    chain: sepolia,
    transport: http(process.env.RPC_URL),
  });

  const walletClient = createWalletClient({
    account: process.env.WALLET_ADDRESS,
    chain: sepolia,
    transport: custom(provider),
  });

  const hash = await walletClient.writeContract({
    address: process.env.USDC_CONTRACT_ADDRESS,
    abi: erc20Abi,
    functionName: "approve",
    args: [
      process.env.PERMIT2_CONTRACT_ADDRESS,
      BitInt(process.env.APPROVAL_AMOUNT),
    ],
  });

  const receipt = await publicClient.waitForTransactionReceipt({ hash });
  return { hash, receipt };
}

/* -------- Example usage with EIP-1193 wallet ---------

// Refer to https://viem.sh/docs/clients/transports/custom and your wallet provider's documentation for the provider object. 
const {hash, receipt} = await approveUSDCWithEIP1193Wallet({provider: window.ethereum});
console.log('Hash:', hash);
console.log('Receipt:', receipt);

---------------------------------- */