how do you parse json rpc errors on frontend?

Question

How do you parse returned json rpc errors from a failed transaction to get the underying revert message if any? I'm on frontend.

example:

try {
    await contract.methods.someMethod().send({from: account})
} catch(e) {
    console.log(e)
}

the error looks like this:

Error: Internal JSON-RPC error.
{
  "code": 3,
  "message": "execution reverted: blah blah",
  "data": "0x12313532492somethingsomething"
}

I need to get the "execution reverted: blah blah" message

---

• I tried:

console.log(e.message)

Internal JSON-RPC error.
{
  "code": 3,
  "message": "execution reverted: blah blah",
  "data": "0x12313532492somethingsomething"
}

console.log(JSON.parse(e))

JSON.parse: unexpected character at line 1 column 1 of the JSON data

Answer 1

My way of resolving this issue is:

Convert the error to string using e.toString() and then removing some chars and converting it to JSON with JSON.parse()

let errore = e.toString() 
if (errore.indexOf('Internal JSON-RPC error.') > -1) {
      errore = errore.replace('\n', '').replace("Error: ", '').replace('Internal JSON-RPC error.', '')
      errore = JSON.parse(errore)
     }

Answer 2

Metamask has an official NPM package for this: https://www.npmjs.com/package/eth-rpc-errors

It is supposed to work like this:

import { serializeError } from "eth-rpc-errors";

try {...} catch (metamaskError) {
    const serializedError = serializeError(metamaskError);
    console.log({ serializedError });
}

However it is currently buggy, the error object is empty: https://github.com/MetaMask/eth-rpc-errors/issues/51

Will update this answer if and when the problem is fixed.

Until then, I also had to manipulate the error string. In my case, the error looked like this:

Error: execution reverted
{
  "originalError": {
    "code": 3,
    "data": "0x233067ae",
    "message": "execution reverted"
  }
}

I managed to format the error data nicely like this (using Ethers.js):

const decodeError = (errRaw) => {
  const errorObject = JSON.parse(
    errRaw.toString().replace("Error: execution reverted", "")
  );

  const abi = require("../pathToAbi.json");

  const iface = new ethers.utils.Interface(abi);

  const errorFragment = iface.getError(errorObject.originalError.data);

  return errorFragment.name;
};