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Ok, I'm new into JS and web3 and MetaMask. I'm still lost about Promise and async/await after reading them for 5 times!

I want to call my smart contract balanceOf method to check if there's enough balance of token before I execute a transfer.

How do I actually wait for this balanceOf value to return to my JS script then only I proceed?

You know, getting the balanceOf takes like only 1 sec, but I know sometimes the user's finger is faster than the brain.

I tried async/await function below but my main code doesn't "wait", it just continues on. I'm using web3 1.0.

Then, I execute the transfer in a separate function. What I'm doing now is firstly I set the token balance using setTokenBalance(balance). Then check if I have enough balance by calling getTokenBalance(). If yes, then I do the transfer. Which works but it's kinda funny cos there's a split second that getTokenBalance shows '0' since it hasn't got the correct balance data.

var tokenBalance = 0;
async function retrieveTokenBalance(contract, walletAddress) {

      await contract.methods.balanceOf(walletAddress).call(function(err,res){
            if(!err){
                console.log(res);
                setTokenBalance(res);
            } else {
                console.log(err);
            }
        });

}

function setTokenBalance(balance) {
    tokenBalance = balance;
}

function getTokenBalance() {
    return tokenBalance;
}
  • 1
    BTW, you should tag your question under web3.js rather than web3j. – goodvibration May 14 at 7:31
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Since your retrieveTokenBalance is an async function, try this...

retrieveTokenBalance(smartContract, walletAddress).then(function(result){

    //If sufficient token
        //Do your token transfer
    //Else
        //Do something else like alerting the user

});

You can learn more about async/await in Javascript here - https://tutorialzine.com/2017/07/javascript-async-await-explained which explains a lot better than other sites.

  • Awesome! It worked. And thanks for the tutorial tip. – warnerque May 16 at 14:03
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Try this:

const balance = await contract.methods.balanceOf(walletAddress).call();
await setTokenBalance(balance);

From your description, it sounds like function setTokenBalance executes a transfer, which means it has to be an async function, hence the await for its completion.

  • The setTokenBalance is just a function to set a variable in JS that stores the token balance. It doesn't do any calls to MetaMask – warnerque May 15 at 11:56
  • @warnerque: So the question in the title makes no sense - "before I execute a transfer" - where exactly in your code are you attempting to execute a transfer??? – goodvibration May 15 at 13:18
  • I execute the transfer in a separate function. The idea is first I set the token balance using setTokenBalance(balance). Then check if I have enough balance by calling getTokenBalance(). If yes, then I do the transfer. – warnerque May 16 at 4:36

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