为什么我的变量仍未定义? [英] Why is my variable still undefined?

问题描述

lastbalance 从未得到定义，因此getBalance函数从不执行其应有的功能.我以为这可能是异步性的问题，但是只有在第一个间隔之前是这样，对吧?有什么想法吗?

lastbalance never get's defined and because of that the function getBalance never does what its supposed to. I thought this might be an issue with asynchronicity but that could only be the case before the first interval, right? Any ideas?

var lastbalance;
getBalance = function (lastbalance, callback){
  btcclient.getBalance('*', 0, function(err, balance) {
    if (err) return console.log(err);
    if (lastbalance != balance || typeof lastbalance == 'undefined'){
      console.log('Last Balance:' + lastbalance);
      var lastbalance = balance;
      updateCauses();
    }
    console.log('Balance:', balance);


    if (typeof callback=='function') callback();

  });
};

setInterval(getBalance, 2000, lastbalance);

推荐答案

两个问题.

1.:.您已将 lastbalance 定义为函数参数...，这在函数的上下文中创建了另一个 lastbalance 变量.取代了在外部作用域中声明的变量.

1.: You defined lastbalance as a function parameter... which created another lastbalance variable in the context of your function... which superseded the variable declared in the outer scope.

var lastbalance; // your outer variable
getBalance = function (lastbalance, callback) { // weeeee, another lastbalance
    btcclient.getBalance('*', 0, function (err, balance) {
        if (err) return console.log(err);
        if (lastbalance != balance || typeof lastbalance == 'undefined') {
            console.log('Last Balance:' + lastbalance);
            var lastbalance = balance;
            updateCauses();
        }
        console.log('Balance:', balance);
        if (typeof callback == 'function') callback();
    });
};

setInterval(getBalance, 2000, lastbalance); //passing lastbalance by value

2.::您使用了 var 在函数中声明了另一个 lastbalance .不要那样做它导致了上述相同的问题.

2.: You used var to declare yet another lastbalance in your function. Don't do that; it caused the same issue described above.

var lastbalance; // your outer variable
getBalance = function (lastbalance, callback) {
    btcclient.getBalance('*', 0, function (err, balance) {
        if (err) return console.log(err);
        if (lastbalance != balance || typeof lastbalance == 'undefined') {
            console.log('Last Balance:' + lastbalance);
            var lastbalance = balance; // here you create a local lastbalance.
                                       // remove the var keyword to refer to
                                       // the original lastbalance
            updateCauses();
        }
        console.log('Balance:', balance);
        if (typeof callback == 'function') callback();

    });
};

setInterval(getBalance, 2000, lastbalance);

最后，您的代码应如下所示:

Finally, your code should look something like this:

var lastbalance;
getBalance = function (/*lastbalance, */callback) { // remove parameter
    btcclient.getBalance('*', 0, function (err, balance) {
        if (err) return console.log(err);
        if (lastbalance != balance || typeof lastbalance == 'undefined') {
            console.log('Last Balance:' + lastbalance);
            /*var*/ lastbalance = balance; // remove var
            updateCauses();
        }
        console.log('Balance:', balance);
        if (typeof callback == 'function') callback();
    });
};

setInterval(getBalance, 2000/*, lastbalance*/); // remove argument

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