Getting unexpected output in Solidity + web3

Question

I have a solidity function:

function something(bytes32 hash) public returns (bool) {
    bool success;
    success = check(hash);
    emit LogSomething(msg.sender, hash, success);
    return success;
}

and I try to show its result on Web3:

contractInstance.something(hash, params, function(error, result){
    if (error) {
        alert("Error!");
    } else {
        $("span#result").text(result);
    }
})

However, in my result span, I get the transaction hash:

0xd0039716e5834ac880f3b66e024c29e4b25cdf69e26b4f19e278f116d6a2fec2

instead of a True or False as expected from a boolean output. Why is this so? There are no error messages whatsoever and I'm confident in the code logic.

Answer 1

You get the actual returned value of a non-constant function (neither pure nor view), only when you call it on-chain (i.e., from another function in this contract or from another function in another contract).

When you call it off-chain (e.g., a web3.js script, a web3.py script, Remix, MyEtherWallet), you get the transaction receipt.

This is because when you call it on-chain, the function has completed its execution by the time it returns, but when you call it off-chain, it is only encapsulated in a transaction and passed to the miners (who may choose to execute it at any time in the future).

Answer 2

Change your javascript to this:

contractInstance.something(hash).call({}, function(error, result){
    if (error) {
        alert("Error!");
    }else {
        console.log(result, 'result');
    }
}

You can read more about .call() web3 method here. Since your smart contract method something is just a get method you don't have to write on the blockchain and it is not needed transaction to be signed and sent to the blockchain. And because of this reason you should add view keyword to method something in your smart contract.