Metamask: Checking ERC721 token approvals in a for loop works in Hardhat Script but fails in React

MetaMask Issue: Checking ERC721 Token Approval in Hardhat Script vs. React

When working with the MetaMask API and Solidity contracts, there are certain edge cases that can lead to unexpected behavior. One common issue is when checking token approvals of ERC721 tokens using a for loop in a Hardhat script vs. React application.

In this article, we will explore the issue and provide solutions to resolve it.

Hardhat Script Issue

In a Hardhat script, you can use the transfer function to transfer ownership of an ERC721 token. When checking token approvals for these contracts using a for loop, you may encounter issues with the approval status being updated correctly.

const contractArr = ['0x1234567890abcdef'];
modifier isApproved(address [] memory contractArr) {;
require (contractArr. length > 0, "LengthZero");
for ( let i = 0; i < contractArr. length; i ++) {;
const tokenAddress = contractArr[i];
contract[tokenAddress]. approve(address. from, address. value);
}}
}}

The problem lies in the fact that when a transfer is made using the transfer function, it returns true immediately after the transaction is processed. However, in the for loop, you need to check whether the approval status is updated correctly.

React to a problem

In a React application, verifying token approvals for ERC721 tokens can be more complicated due to the asynchronous nature of the API calls.

import {contract} from './contracts/ERC721.sol';
import Web3 from 'web3';
const contractArr = ['0x1234567890abcdef'];
function isApproved(address) {
const web3 = new Web3(window.ethereum);
return contract. ERC721. (contract. address, address. value);
}}

In this React example, the isApproved function uses the contract object from Solidity contracts to check if the token has been approved.

Solution

To resolve these issues in both Hardhat scripts and React applications, you can use a different approach:

• Use the transfer function with an event emitter: Instead of checking the approval status directly, use the eventTransferComplete event emitted by the MetaMask API to update the state of your contract.

const contractArr = ['0x1234567890abcdef'];
modifier isApproved (address [] memory contractArr) {;
require (contractArr. length > 0, "LengthZero");
for ( let i = 0; i < contractArr. length; i ++) {;
const tokenAddress = contractArr[i];
eventTransferComplete(tokenAddress).emit('approval', { status: true });
// Update the status of the contract
contract[tokenAddress]. approve(address. from, address. value);
}}
}}

• Use a callback function in the transfer event: You can also pass a callback function to the transfer event emitted by MetaMask that will be called when the approval status is updated.

const contractArr = ['0x1234567890abcdef'];
eventTransferComplete(tokenAddress).on('approval', (status) => {
if ( status . status === true ) {
// Update the status of the contract
contract [tokenAddress]. approve (address. from, address. value);
}}
});

Using these approaches, you can ensure that your contracts are properly validated for token approvals in both Hardhat scripts and React applications.

Conclusion

When working with the MetaMask API and Solidity contracts, it is important to be aware of potential issues, such as validating token approvals for ERC721 tokens. By understanding the basic mechanics of the “transfer” function and using event emitters or callback functions, you can resolve these issues in both Hardhat scripts and React applications.