app.js

var someName = {   
    balance: 0
};

function deposit(account, amount){
    account.balance += amount;
}
function withdraw(account, balance){
    account.balance -= balance;
}
function getBalance(account){
    console.info(account.balance);
}

deposit(someName, 3000);
withdraw(someName, 400);
getBalance(someName);