What is the correct way to access public variable from contract in Truffle: then or standard callback?

Question

There are some similar posts to this but none seem to be able to solve my problem.

I have a contract deployed with Truffle running with testrpc.

I want to access the value of a public uint variable named gameStatus defined in the deployed contract game variable as such:

uint public gameStatus = 23;

I have found two ways to do this:

game.gameStatus(function(err, res){
    document.getElementById('amt').innerText = res;
});

And using the then operator from Promises.

game.gameStatus().then(function(result){
    document.getElementById('tableamt').innerText = result;
});

The first method never affects the value of 'tableamt' in the HTML. And the second method always yields a value of '0' in the HTML.

The contract in both cases deploys without errors and web3 does not complain.

Any help is much appreciated.

Thanks!

Have you tried web3.eth.getCode(contractAddress) and confirmed the contract is indeed deployed? — Xavier Leprêtre B9lab, Jan 17 '17 at 16:41
Trying to do that gives me the following error:
Uncaught Error: The MetaMask Web3 object does not support synchronous methods like eth_getCode without a callback parameter.

However when I do game.deployed() I get this:

Contract BettingOver : () address : "0x7881c3a33335a8cceb04b86131f4bf43db26dbd8" allEvents : () betEnd : () bettingEnd : () bettingStart : ()

So it looks like the variables are not being set during deploy? — Carlos G. Oliver, Jan 17 '17 at 17:20
Then that should do web3.eth.getCode(contractAddress, function(err, code) { console.log(code);}) — Xavier Leprêtre B9lab, Jan 17 '17 at 17:24
web3.eth.getCode("0x7881c3a33335a8cceb04b86131f4bf43db26dbd8", function(err, code){ console.log(code)}); undefined VM245:1 0x — Carlos G. Oliver, Jan 17 '17 at 17:33
0x means there is no code at the address. Of course your "functions" return 0. — Xavier Leprêtre B9lab, Jan 17 '17 at 17:50
hmm i see. so you think it's that the function was not deployed correctly? — Carlos G. Oliver, Jan 17 '17 at 19:34
I have the following in a file in the migrations/ folder: module.exports = function(deployer) { deployer.deploy(Modgame, 10, 120, 120); deployer.autolink();}; and when I run truffle migrate it says that the migration was done successfully. — Carlos G. Oliver, Jan 17 '17 at 19:38
Strange, to me it looks very much like there is a crash in your constructor, or a parent constructor. We need to see code at this stage. — Xavier Leprêtre B9lab, Jan 17 '17 at 22:01

score 9 · Answer 1 · edited Apr 13 '17 at 13:01

9

To get public variable value you need to use call. It is evaluated directly on local node without sending transaction to the blockchain. See also this great answer.

So, you need to call it that way:

game.gameStatus.call(function(err, res){
    document.getElementById('amt').innerText = res;
});

edited Apr 13 '17 at 13:01

Community

1

answered Jan 17 '17 at 19:24

max taldykin

2,966
19
27

Jerry Lin · Answer 2 · 2019-07-01T16:48:15.060

8

It's different now. You should use contractName.methods.varName().call(callback) to access state variables in web3 1.0.0. Solidity compiler automatically creates getters for public state variables.

To answer your question, the method call should be:

game.methods.gameStatus().call(function(err, res){
    //do something with res here
    console.log(res); //for example
};

edited Jul 01 '19 at 16:48

answered Mar 18 '18 at 23:03

Jerry Lin

81
1
3

score 1 · Answer 3 · answered Mar 06 '22 at 17:25

1

This

(await game.gameStatus()).toString()

or this

game.gameStatus().then((x) => x.toString())

works for me.

answered Mar 06 '22 at 17:25

user66081

131
3

score 1 · Answer 4 · answered Oct 04 '18 at 06:00

A simple promise works just fine.

game.gameStatus().then(function (result) {
    console.log(result);
})

game is the loaded contact, which in my case, I get with another promise.

App.contracts.GameContract.deployed().then(function (game) {
    return game.winningNumbers();
}).then(function (result) {
    console.log(result);
})

What is the correct way to access public variable from contract in Truffle: then or standard callback?

4 Answers4

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