Ethereum: How to display custom Solidity errors on the front-end? - F.I.S.A.R. A.P.S.

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Displaying Solidity’s Custom Errors on the Frontend

When building complex decentralized applications (dApps), it’s not uncommon to encounter custom errors that can’t be caught by traditional error handling mechanisms. In this article, we’ll explore how to display these custom errors on the frontend using Ethereum’s web3.js library.

Why Display Custom Errors?

Custom errors are often the result of unexpected logic in your contract or third-party integrations. By displaying them on the frontend, you can:

• Improve user experience: Users will appreciate a clear indication that something went wrong.

• Enhance debugging tools: Developers can use these custom errors to identify and fix issues more efficiently.

Prerequisites

Before we dive in, make sure you have:

• A basic understanding of Solidity and web3.js

• A contract deployed on the Ethereum blockchain

Displaying Custom Errors with web3.js

In this example, we’ll use web3.js to display custom errors in a frontend application. We’ll create an event emitter that listens for CustomError events emitted by your contract.

First, install web3.js and w3-logger libraries:

npm install web3 w3-logger

Contract Implementation

pragma solidity 0.8.16;
contract Test {
    event CustomError(uint256 value);
    uint public a;
    constructor() public {
        emit CustomError(10); // Example error code
    }
    function testFunction() external pure returns (bool) {
        a = 5; // This should trigger a custom error
        return true; // Successful execution
    }
}

Frontend Implementation

import * as w3 from "web3";
import { Events } from "w3-logger";
class FrontendApp {
  constructor(w3Instance) {
    this.w3 = w3Instance;
    const eventEmitter = new Events();
    eventEmitter.on("CustomError", (errorValue) => {
      console.error(Custom Error: ${errorValue});
      // Handle custom error logic here
    });
    // Deploy contract
    deployContract(w3Instance);
  }
  async deployContract(w3Instance) {
    const contractAddress = "0x..."; // Replace with your contract address
    const contractAbi = "..."; // Replace with your contract ABI
    const web3 = new w3.Web3(w3Instance, contractAbi);
    await web3.eth.deployContract(contractAddress);
  }
}

Running the Frontend

To run this frontend application, you’ll need to create a new Solidity contract and deploy it. Then, import the FrontendApp class and call its constructor.

const w3Instance = require("web3")("
const frontendApp = new FrontendApp(w3Instance);

Custom Error Handling

In your frontend application, you can handle custom errors using a try-catch block:

try {
  const result = await frontendApp.testFunction();
  console.log(result);
} catch (error) {
  console.error(Custom Error: ${error.message});
}

By displaying custom errors on the frontend, you can improve your application’s user experience and make it easier for developers to identify and fix issues.

Conclusion

Displaying custom errors is an essential step in building robust decentralized applications. By using web3.js and implementing a custom error handling system, you can enhance your frontend application’s usability and debugging capabilities. This example demonstrates how to deploy a contract on the Ethereum blockchain and display custom errors on the frontend using web3.js.