Write (Fee Delegation)

You can make a "transaction" that including payment request to feepayer when you want to execute the Smart Contract.

Import the @kaiachain/viem-ext packages to add kaia features on web3

Initializes a public client for read-only interactions with the Kaia blockchain.

Set up sender and fee payer wallets using createWalletClient, configured with the Kairos chain, an HTTP transport, and the sender’s private key converted to an account.

Set the contract address you want to execute into the to field and set ABI.

Encode the function name and parameter with the encodeFunctionData function

Create a transaction request for write a smart contract using prepareTransactionRequest, specifying the sender’s account, recipient address, value to transfer (0 KLAY in this example) and transaction type (TxType.SmartContractExecution)

Signing the transaction with the wallet client’s signTransaction method.

The sender submits the transaction to the Kaia blockchain using klay_sendRawTransaction, and the result (typically a transaction hash) is logged. The sender pays the transaction fees.

Prepares a fee-delegated transaction (FeeDelegatedSmartContractExecution) to call the same setNumber function on the contract. The setup is similar to the non-fee-delegated transaction, but the fee payer signs the transaction to cover the fees.

The sender signs the transaction first, the fee payer adds their signature, and the transaction is submitted to the Kaia blockchain.

Uses the public client to read the value of the number variable from the contract by calling the number function (a view function that doesn’t modify state).

writeWithFeeDelegation.js


import {
    http,
    encodeFunctionData,
    createWalletClient, createPublicClient, kairos,
    TxType,
    privateKeyToAccount
} from "@kaiachain/viem-ext";
const publicClient = createPublicClient({
    chain: kairos,
    transport: http(),
});
const senderWallet = createWalletClient({
    chain: kairos,
    transport: http(),
    account: privateKeyToAccount(
        "0x0e4ca6d38096ad99324de0dde108587e5d7c600165ae4cd6c2462c597458c2b8"
    ),
})
const feePayerWallet = createWalletClient({
    chain: kairos,
    transport: http(),
    account: privateKeyToAccount(
        "0x9435261ed483b6efa3886d6ad9f64c12078a0e28d8d80715c773e16fc000cff4"
    ),
});
// Example usage
(async () => {
    const contractAddr = "0x95Be48607498109030592C08aDC9577c7C2dD505";
    const abi = [{ "inputs": [{ "internalType": "uint256", "name": "initNumber", "type": "uint256" }], "stateMutability": "nonpayable", "type": "constructor" }, { "anonymous": false, "inputs": [{ "indexed": false, "internalType": "uint256", "name": "number", "type": "uint256" }], "name": "SetNumber", "type": "event" }, { "inputs": [], "name": "increment", "outputs": [], "stateMutability": "nonpayable", "type": "function" }, { "inputs": [], "name": "number", "outputs": [{ "internalType": "uint256", "name": "", "type": "uint256" }], "stateMutability": "view", "type": "function" }, { "inputs": [{ "internalType": "uint256", "name": "newNumber", "type": "uint256" }], "name": "setNumber", "outputs": [], "stateMutability": "nonpayable", "type": "function" }];
    const data = encodeFunctionData({
        abi,
        args: [123n],
        functionName: "setNumber",
    });
    // non fee payer
    const tx = await senderWallet.prepareTransactionRequest({
        type: TxType.SmartContractExecution,
        account: senderWallet.account,
        to: contractAddr,
        value: 0,
        data,
    });
    console.log("preparedTx", tx);
    const signedTx = await senderWallet.signTransaction(tx);
    const sentTx = await senderWallet.request({
        method: "klay_sendRawTransaction",
        params: [signedTx],
    });
    console.log("contract interaction tx", sentTx);
    // fee payer
    const tx2 = await senderWallet.prepareTransactionRequest({
        type: TxType.FeeDelegatedSmartContractExecution,
        account: senderWallet.account,
        to: contractAddr,
        value: 0,
        data,
    });
    const signedTx2 = await senderWallet.signTransaction(tx2);
    const feePayerSignedTx = await feePayerWallet.signTransactionAsFeePayer(
        signedTx2
    );
    const sentFeePayerTx = await feePayerWallet.request({
        method: "klay_sendRawTransaction",
        params: [feePayerSignedTx],
    });
    console.log("fee payer contract execution tx", sentFeePayerTx);
    const result = await publicClient.readContract({
        address: contractAddr,
        abi,
        functionName: 'number'
    })
    console.log('Current contract value', result);
})();

output


❯ js writeWithFeeDelegation.js
preparedTx {
  type: 48,
  account: {
    address: '0xA2a8854b1802D8Cd5De631E690817c253d6a9153',
    nonceManager: undefined,
    sign: [AsyncFunction: sign],
    signAuthorization: [AsyncFunction: signAuthorization],
    signMessage: [AsyncFunction: signMessage],
    signTransaction: [AsyncFunction: signTransaction],
    signTypedData: [AsyncFunction: signTypedData],
    source: 'privateKey',
    type: 'local',
    publicKey: '0x04dc9dccbd788c00fa98f7f4082f2f714e799bc0c29d63f04d48b54fe6250453cdaf06ca34ae8714cf3dae06bacdb78c7c2d4054bd38961d40853cd5f15955da79'
  },
  to: '0x95Be48607498109030592C08aDC9577c7C2dD505',
  value: 0,
  data: '0x3fb5c1cb000000000000000000000000000000000000000000000000000000000000007b',
  from: '0xA2a8854b1802D8Cd5De631E690817c253d6a9153',
  nonce: 2400,
  chainId: 1001,
  gas: 27893n,
  gasPrice: '0x66720b300',
  gasLimit: 69732
}
contract interaction tx 0x67e3975188a4e7c221ac823450b51a4ac8064ddeb35523defd890b1559e0343d
fee payer contract execution tx 0xc63d64d49a95ecc9f0fa9a25e78a7df5192224d703f634a77a64123ed36ac97f
Current contract value 123n