Elegant way to map web3.js error messages

Question

when user's transaction fails before submitting to the blockchain, I want to know the failure reason, so I can give a better user experience.

for example if user rejects a transaction in Metamask, or if the transaction fails due to insufficient funds for gas. how can I detect that?

my current implementation is not great, and will break easily. is there more elegant way to do it?

return sendTransaction(txData).catch(err => {
    if (err.message.includes('User denied transaction') ||
        err.message.includes('Request has been rejected.') ||
        err.message.includes('transaction has been discarded') ||
        err.message.includes('Transaction not confirmed'))
        throw new Error('web3UserTxRejected');

    if (err.message.includes('nonce too low'))
        throw new Error('web3NonceTooLow');

    if (err.message.includes('nonce may not be larger than'))
        throw new Error('web3NonceTooHigh');

    if (err.message.includes('insufficient funds for gas'))
        throw new Error('web3InsufficientFundsForGas');

    if (err.message.includes('intrinsic gas too low'))
        throw new Error('web3GasTooLow');

    throw new Error(err);
});

Answer 1

Currently there is no standard API return values for errors for web3.js implementations (somebody please correct me if I am wrong).

• MetaMask is free to change the error message strings as they wish

• Error messages can be localized

• Other wallets like Parity, Status.im, Trust give different error message

I feel the JavaScript design patterns are partly to blame here; JavaScript design patterns do not encourage good user facing error handling.

I suggest this could be addressed by opening the discussion on web3.js Github issue tracked and propose how the error handling should be done.