How to get the returned values in Solidity functions?

Question

Imagine I'm developing a simple function as the following:

       uint256 state;  
       event Addition(uint256 result);
   function addition(uint256 a, uint256 b)
        public       
        returns (uint256)
    {

        uint256 result = a + b;
        state = result;
        emit Addition(result);       

        return result;
    }

How can I get the returned value (result)? I know that I can get the value listening the event Addition, but in that case... Why should I return values? When I execute the function with web3.js in my javascript frontend, I can wait until the transaction finishes, but the result don't came with transaction response.

Not possible for transactions. ‚Return‘ works only between contract interaction. You can use events and then search the log in the transactionReceipt — Majd TL, May 18 '22 at 11:52
Listening from another Smart Contract makes sense for the return value ;) — Alexander Herranz, May 18 '22 at 12:07

score 1 · Answer 1 · answered May 18 '22 at 09:08

I believe the problem you're describing is because you are trying to get a return variable from a function which is marked as non-static (not pure/view). Unfortunately, as far as I can tell, it's not possible to get a function result from a mined transaction.

However, you should be able to tell web3js to evaluate this function in a static context. With ethersjs this is .callstatic. With web3js this might mean that (not too familiar with web3js) you use .call instead of .send in order to get a function result.

score 1 · Answer 2 · answered May 18 '22 at 11:53

1

Your function is neither pure nor view so it returns transaction receipt instead of the return value. This function would return result:

   function addition(uint256 a, uint256 b)
        public
        pure    
        returns (uint256)
    {
    uint256 result = a + b;

    return result;
}

answered May 18 '22 at 11:53

MantasFam

327
3
13

Yes sure, but I was talking in case of not view/pure functions (I created/modified a state variable to better illustrate the example). – Alexander Herranz May 18 '22 at 12:07

How to get the returned values in Solidity functions?

2 Answers2