Question

lastbalance永远不会被定义，因此函数getBalance永远不会做它应该做的事情。我认为这可能是异步性问题，但只能是第一个间隔之前的情况，对吗？有什么想法吗？

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);

Answer 1

两个问题。

1。：您将lastbalance定义为函数参数...它在您的函数上下文中创建了另一个lastbalance变量...这取代了声明的变量在外部范围内。

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var在您的函数中声明了另一个lastbalance。不要那样做;它引起了上述同样的问题。

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：

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

Answer 2

你有很多lastBalance个变量！

外部范围var lastBalance =
getBalance函数中的一个（参数名称）
回调函数var lastBalance =

这意味着当您在内部函数中执行lastBalance =时，只会设置第三个变量。没有代码可以在外部范围内设置变量。每次运行函数时，内部范围中的一个都设置为undefined。

我很确定你只想要一个变量。你需要做这样的事情：

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

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

setInterval(getBalance, 2000);

这可能不完全正确，因为我不熟悉您的API，但它可能没有太大的错误。

Answer 3

所以这里有3个名为lastbalance的不同变量，javascript将使用范围最窄的变量。

var lastbalance;  
//creating a lastbalance var in the global scope (a member of the window object)

getBalance = function (lastbalance, callback){ 
    // <- create a function with a parameter of lastbalance. 
    // this one is a member of this getBalance function 
    // (functions in javascript are first class citezens i.e. 
    // objects too) and is different the the memeber of the 
    // window object called lastbalance.

    // that is  -- window['lastBalance'] != window.getBalance['lastBalance']; 

    var lastbalance = something   
    // create ANOTHER parameter lastbalance this time a member of the      
    // current code block, and not the same as the window member or
    // the function memeber. 

      // that is window['lastBalance'] 
      // != window.getBalance['lastBalance']
      // != window.getBalance.body['lastBalance']
};

你想要的东西看起来更像是这样。

//Create a global value. 
var lastBalance; 
getBalance = function (callback){
//this function doesnt need to be passed a variable it can read from the global scope. 
    btcclient.getBalance('*', 0, function(err, balance) {
        if (err) return console.log(err);
        if (lastbalance != balance || typeof lastbalance == 'undefined'){
            console.log('Last Balance:' + lastbalance);
            lastbalance = balance;  // JS will work its way back and the only last balance is in the 
                                    // window object, so it will use that, no need to pass it a 
                                    // reference, just address it globablly. 

            updateCauses();
         }
         console.log('Balance:', balance);
         if (typeof callback=='function') callback();
    });
};

setInterval(getBalance, 2000);

为什么我的变量仍未定义？

3 个答案: