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Ethereum: Polygon zk-EVM Get Token Balance Error

Overview

The Ethereum Virtual Machine (EVM) and Zk-SNARKs (zk-Edward Key-Share Proofs) are powerful tools for building secure and scalable decentralized applications (dApps). However, integrating these concepts with the Ethereum blockchain can be challenging due to their different architectures. In this article, we’ll explore why you’re encountering an error when trying to get the balance of every ERC-20 token in the Polygon zk-EVM network using Ethers.js.

The Issue

When working with ERC-20 tokens on the Polygon zk-EVM network, you encounter a “could not decode result data” error. This error occurs because the ethers.js library is unable to parse the result of the getBalance() function call, which is used to retrieve the balance of an ERC-20 token.

The Problem

The issue arises from the fact that the getBalance() function returns a JSON object containing the balance data. However, Ethers.js expects this object to be in a specific format, where it can successfully decode and parse the result. Unfortunately, the ethers.js library is unable to handle the resulting JSON data due to its internal implementation.

Solution

To resolve this issue, you have a few options:

1. Update Ethers.js to Version 5.x

The most straightforward solution is to update Ethers.js to version 5.x or later, which includes improved support for ERC-20 token balances on the ZK-EVM network.

npm install ethers@latest

2. Use the getBalance() function with a custom decoding function

Another solution is to create a custom decoding function that can handle the resulting JSON data from the getBalance() function call.

Here’s an example implementation:

const { ethers } = require ( ' ethers ' ) ;


async function getBalance ( tokenAddress ) { .

  const balance = await ethers.getBalance(tokenAddress);

  return new Promise ( ( resolve , reject ) => { return new Promise ( ( resolve , reject ) => {

    try {

      resolve(balance.data.toString());

    } catch (error) {

      reject ( error ) ;

    } }

  });

} }


getBalance("0x...").then((balance) => {

  console.log(balance); // Output: the balance data as a string

}).catch((error) => {

  console.error(error);

});

In this example, we define a custom getBalance() function that takes a token address and returns a promise that resolves to the balance data as a string. This allows us to handle the resulting JSON data successfully.

Conclusion

By updating Ethers.js to version 5.x or creating a custom decoding function, you should be able to resolve the “could not decode result data” error when getting the balance of every ERC-20 token in the Polygon zk-EVM network using Ethers.js.