Handling native tokens with 0x Swap API

When using the 0x Swap API to handle native tokens like ETH, the process differs from ERC-20 tokens. Here’s what you need to know to handle native tokens properly:

1. Skip the allowance check: Unlike ERC-20 tokens, native tokens do not require an allowance or approval step. Therefore, you can skip the approve() call when preparing to send native tokens.

2. Set the transaction value: Ensure that the value field in your transaction parameters accurately reflects the amount of native token (in wei) you intend to send.

tip

⚡️ Quicklink

See a full Swap API headless example that demonstrates how to handle native tokens. See the running instructions here.

Code example

Here's a code snippet of how you can implement the above steps:

import { createWalletClient, http, parseEther, sendTransaction } from 'viem';
import { privateKeyToAccount } from 'viem/accounts';
import { mainnet } from 'viem/chains';

// Create a wallet client using your private key
const account = privateKeyToAccount('YOUR_PRIVATE_KEY');

const client = createWalletClient({
    account,
    chain: mainnet,
    transport: http('https://eth-mainnet.g.alchemy.com/v2/YOUR_ALCHEMY_KEY'), // Provide an authenticated RPC URL to avoid rate-limiting
});

// Check if the sellToken is a native token (ETH) to skip the allowance check
if (eth.address === '0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE') {
    console.log('Native token detected, no need for an allowance check');
} else {
    // Check if allowance is required for non-native tokens
    if (price.issues.allowance !== null) {
        try {
            const { request } = await eth.simulate.approve([price.issues.allowance.spender, maxUint256]);
            // Remainder of code...
        } catch (error) {
            console.error('Error approving token:', error);
        }
    }
}

// Check if it's a native token (like ETH)
if (eth.address === '0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE') {
    const nonce = await client.getTransactionCount({
        address: client.account.address,
    });

    // Directly sign and send the native token transaction
    const txHash = await client.sendTransaction({
        account: client.account,
        chain: client.chain,
        gas: quote?.transaction.gas ? BigInt(quote.transaction.gas) : undefined,
        to: quote?.transaction.to,
        data: quote.transaction.data,
        value: BigInt(quote.transaction.value), // Ensure value is set for native tokens
        gasPrice: quote?.transaction.gasPrice ? BigInt(quote.transaction.gasPrice) : undefined,
        nonce: nonce,
    });

    // Log the transaction hash
    console.log('Transaction sent:', txHash);
}