How to detect solidity errors in ether js

Question

After using a function in solidity with ether js, if that function fails, how can I detect this error with ether js?

error error_name();
contract example(){

  function f(){
    revert error_name();
  }
}

Answer 1

Here's how you can detect your error with ethers.js quite easily using ethers-decode-error.

Install ethers-decode-error in your project:

npm install ethers-decode-error --save

Next, the following code will help you get the name of the custom error in your solidity contract:

import { ErrorDecoder, DecodedError } from 'ethers-decode-error'

// This is the instance of your example smart contract
const exampleContract = new ethers.Contract('0x1234', abi, provider)

const errorDecoder = ErrorDecoder.create([exampleContract.interface])

try {
  const tx = await exampleContract.f()
  await tx.wait()
} catch (err) {
  const decodedError = await errorDecoder.decode(err)

  // Prints "error_name" which is what you have named the error in your contract
  console.log('Custom error name:', decodedError.name)

  const reason = customReasonMapper(decodedError)
  // Prints "This is a custom message for error_name from example contract."
  console.log('Custom error message:', reason)
}

const customReasonMapper = ({ name, reason }: DecodedError): string => {
  switch (name) {
    case 'error_name':
      return 'This is a custom message for error_name from example contract.'

    // You can match other custom errors you may have in your contract here...
    // case 'MyOtherError': ...

    // Captures other error messages
    default:
      return reason ?? 'There was an error'
  }
}

You can find more examples for handling solidity custom errors here. :)

Answer 2

On frontend:

const [error, setError] = useState();

const call = () => {
 try{
 //ethers logics
}catch(err){
 setError(err)
}
}