How to get a value from a “Promise” object

Question

I started learning ethereum and web3js and noticed some functions on Web3js are asynchronous. What i want to achieve is get the account balance of a wallet and use the data for

Answer 1

You need to await the promised values. You can do this with another then call, and -- to avoid one request having to wait for the previous one to finish -- Promise.all:

function interTransfer(){
    // ...
    promise = Promise.all([getAccountBalance2(from), getAccountBalance2(to)])
        .then(function ([fromWallet, toWallet]) {
            console.log('from wallet', fromWallet, 'to wallet', toWallet); 
        });
    // ...
    return promise; // the caller will also need to await this if it needs the values
}

Or, with an async function and the await keyword:

function async interTransfer(){
    // ...
    [fromWallet, toWallet] = 
        await Promise.all([getAccountBalance2(from), getAccountBalance2(to)]);
    console.log('from wallet', fromWallet, 'to wallet', toWallet); 
    // ...
    return [fromWallet, toWallet]; // caller's promise now resolves with these values
}

Note that the return in the getBalance callback is useless, and you should probably call reject with a reason in the case of if(error).