lkt/approve.mjs

import Web3 from "web3";
import { BigNumber } from "bignumber.js";
import { Wallet, Provider } from "zksync-web3";
import erc20Abi from "./erc20Abi.json" assert { type: "json" };
import { ethers } from "ethers";

const rpc = "https://zksync2-testnet.zksync.dev/";
const privateKey = "0xd768b0b3f8dedcb465ad680268453391f7da6ec4e1942a13fdfcdea8773aab3e";
const tokenAddress = "0xB2bAbfBBB09A17Fb38cBc7E793B18078dd241347";
const spender = "0x6eeF3310E09DF3aa819Cc2aa364D4f3Ad2E6fFe3";

const provider = new Provider(rpc);
const wallet = new Wallet(privateKey).connect(provider);
const web3 = new Web3(new Web3.providers.HttpProvider(rpc));

const token = new web3.eth.Contract(erc20Abi, tokenAddress);
const decimals = await token.methods.decimals().call();
console.log(`decimals: ${decimals}`);
const allowance = await token.methods.allowance(wallet.address, spender).call();
console.log(`allowance: ${ethers.utils.formatUnits(allowance, decimals)}`);
if (!new BigNumber(allowance).isGreaterThan(new BigNumber(0))) {
    const approve = token.methods.approve(spender, ethers.constants.MaxUint256.toHexString());
    const gasLimit = await approve.estimateGas({ from: wallet.address });
    console.log(`gasLimit: ${gasLimit}`);
    const tx = await wallet.sendTransaction({
        to: tokenAddress,
        data: approve.encodeABI(),
        gasLimit: parseInt(new BigNumber(gasLimit).times(new BigNumber(0.5)).toFixed(0) ),
    });
    console.log(tx);
}