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

MetaMask Issue: Verifying ERC721 Token Approvals in Hardhat Script vs React

When working with the MetaMask API and Solidity contracts, there are some edge cases that can cause unexpected behavior. One common issue is when verifying token approvals for ERC721 tokens using a for loop in a Hardhat script versus a React application.

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

Hardhat Script Issue

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

const contractArr = ['0x1234567890abcdef'];
modifier is Approved(address[] memory contractArr) {
require(contractArr.length > 0, "Length Zero");
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 performing a transfer using the “transfer” function, it returns the value “true” immediately after processing the transaction. However, in the for loop, you need to check whether the approval status is updated correctly.

React to the 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.isApproved(contract.address, address.value);
}

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

Solution

To solve these problems 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 the contract.

const contractArr = ['0x1234567890abcdef'];
modifier is Approved(address[] memory contractArr) {
require(contractArr.length > 0, "Length Zero");
for (let i = 0; i < contractArr.length; i++) {
const tokenAddress = contractArr[i];
eventTransferComplete(tokenAddress).emit('approval', { status: true });
// Update the contract state
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, which will be called when the approval status is updated.

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

Using these approaches, you can ensure that your contracts are properly validated for token approval 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 validation of ERC721 token approvals. By understanding the underlying mechanics of the transfer function and using event emitters or callback functions, you can solve these issues in both Hardhat scripts and React applications.

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