How to display Custom Error in Frontend or custom tests?

Question

I am using custom error like these:

error BadIndexError();

revert BadIndexError();

Now, if I want to retrieve these errors how would I retrieve it in frontend?

Plus, I am using custom framework for tests for my company. How would I retrieve such errors in my tests as well? Right now I just get revert and no error message.

Any simple way? Does ethersjs support it?

Answer 1

I have some posts about custom errors in my blog.

for Ethers.js: https://blog.emn178.cc/en/post/ethers-js-parse-custom-error/

for Web3.js: https://blog.emn178.cc/en/post/using-web3-js-to-parse-custom-error/

If you use hardhat for testing, you can check document, usage will looks like

await expect(
 contract.someMethod()
).to.be.revertedWithCustomError(contract, 'BadIndexError');

If you use custom framework for tests, you may use parseCustomError function mentioned in my blog and check its name and args.