viem

# Viem for Celo Viem is a lightweight TypeScript library with first-class Celo support. It powers wagmi and RainbowKit. Source: https://viem.sh/docs/chains/celo ## When to Use - Building dApps that interact with Celo - Sending transactions with alternative fee currencies - Reading contract state and blockchain data - Signing messages and transactions ## Installation ```bash npm install viem ``` ## Chain Configuration Source: https://github.com/wevm/viem (chain definitions) ### Mainnet ```typescript import { celo } from "viem/chains"; // Chain ID: 42220 // RPC: https://forno.celo.org // Explorer: https://celoscan.io ``` ### Testnet (Celo Sepolia) ```typescript import { celoSepolia } from "viem/chains"; // Chain ID: 11142220 // RPC: https://forno.celo-sepolia.celo-testnet.org // Explorer: https://celo-sepolia.blockscout.com ``` ### Custom Chain with Celo Config ```typescript import { defineChain } from "viem"; import { chainConfig } from "viem/celo"; export const customCeloChain = defineChain({ ...chainConfig, id: 42220, name: "Custom Celo", // ... }); ``` ## Client Setup ### Public Client (Read Operations) ```typescript import { createPublicClient, http } from "viem"; import { celo } from "viem/chains"; const publicClient = createPublicClient({ chain: celo, transport: http(), }); // Read contract state const balance = await publicClient.getBalance({ address: "0x...", }); ``` ### Wallet Client (Write Operations) ```typescript import { createWalletClient, custom } from "viem"; import { celo } from "viem/chains"; const walletClient = createWalletClient({ chain: celo, transport: custom(window.ethereum), }); const [address] = await walletClient.getAddresses(); ``` ## Fee Currency Support Celo allows paying gas fees in tokens other than CELO. Use whitelisted fee currency adapters. Source: https://viem.sh/docs/chains/celo ### Fee Currency Addresses - Mainnet | Token | Adapter Address | |-------|-----------------| | USDC | 0x2F25deB3848C207fc8E0c34035B3Ba7fC157602B | | USDT | 0x0e2a3e05bc9a16f5292a6170456a710cb89c6f72 | ### Fee Currency Addresses - Celo Sepolia | Token | Adapter Address | |-------|-----------------| | USDC | 0x4822e58de6f5e485eF90df51C41CE01721331dC0 | ### Serialize Transaction with Fee Currency ```typescript import { serializeTransaction } from "viem/celo"; import { parseGwei, parseEther } from "viem"; const serialized = serializeTransaction({ chainId: 42220, gas: 21001n, feeCurrency: "0x2F25deB3848C207fc8E0c34035B3Ba7fC157602B", // USDC adapter maxFeePerGas: parseGwei("20"), maxPriorityFeePerGas: parseGwei("2"), nonce: 69, to: "0x1234512345123451234512345123451234512345", value: parseEther("0.01"), }); ``` ### Send Transaction with Fee Currency ```typescript import { createWalletClient, custom, parseEther } from "viem"; import { celo } from "viem/chains"; const USDC_ADAPTER = "0x2F25deB3848C207fc8E0c34035B3Ba7fC157602B"; const walletClient = createWalletClient({ chain: celo, transport: custom(window.ethereum), }); const [address] = await walletClient.getAddresses(); // Send transaction paying gas in USDC const hash = await walletClient.sendTransaction({ account: address, to: "0x...", value: parseEther("1"), feeCurrency: USDC_ADAPTER, }); ``` ### Contract Call with Fee Currency ```typescript const hash = await walletClient.writeContract({ address: CONTRACT_ADDRESS, abi: CONTRACT_ABI, functionName: "transfer", args: [recipient, amount], feeCurrency: USDC_ADAPTER, }); ``` ## Celo Utilities ### Parse Transaction ```typescript import { parseTransaction } from "viem/celo"; // Supports CIP-64, EIP-1559, EIP-2930, and Legacy transactions const transaction = parseTransaction("0x7cf846..."); ``` ### Serialize Transaction ```typescript import { serializeTransaction } from "viem/celo"; const serialized = serializeTransaction({ chainId: 42220, feeCurrency: "0x2F25deB3848C207fc8E0c34035B3Ba7fC157602B", // ... other params }); ``` ## Reading Contract Data ```typescript import { createPublicClient, http } from "viem"; import { celo } from "viem/chains"; const publicClient = createPublicClient({ chain: celo, transport: http(), }); const ERC20_ABI = [ { name: "balanceOf", type: "function", stateMutability: "view", inputs: [{ name: "account", type: "address" }], outputs: [{ type: "uint256" }], }, ] as const; const balance = await publicClient.readContract({ address: "0x765de816845861e75a25fca122bb6898b8b1282a", // USDm abi: ERC20_ABI, functionName: "balanceOf", args: ["0x..."], }); ``` ## Multicall Batch multiple read calls efficiently: ```typescript const results = await publicClient.multicall({ contracts: [ { address: TOKEN_ADDRESS, abi: ERC20_ABI, functionName: "balanceOf", args: [userAddress], }, { address: TOKEN_ADDRESS, abi: ERC20_ABI, functionName: "totalSupply", }, ], }); ``` ## Important Notes - Viem is the recommended library for Celo (ethers.js and web3.js don't support `feeCurrency`) - Fee currency transactions use type `0x7b` (CIP-64) - Transactions with fee currencies incur ~50,000 additional gas - Omitting `feeCurrency` defaults to paying in CELO - Use `viem/celo` for Celo-specific utilities (parseTransaction, serializeTransaction) ## Dependencies ```json { "dependencies": { "viem": "^2.0.0" } } ``` ## Additional Resources - [fee-currencies.md](references/fee-currencies.md) - Complete fee currency reference