javascript - 从循环或条件内更新变量

我正在尝试像这样从循环内部更新循环外部存在的变量：

var firstRun = true;
console.log("firstRun is " + firstRun);
if(firstRun == true){
    console.log("This is your first run");
    firstRun = false;
}else{
    console.log("You have already run this loop at least once");
};

假设此代码块在可以运行4次的较大代码块之内，我希望它输出一次This is your first run，然后输出You have already run this loop at least once 3次。相反，我得到This is your first run 4次，并且console.log("firstRun is " + firstRun);始终输出true

我确定这是我不太了解的范围问题。原谅我，我来自露比（Ruby）:)

最佳答案

您要在循环的每个步骤中重新声明firstRun。将var firstRun = true;移出循环。

如果无法将其移出循环，则必须使用一个对象，并在分配该对象之前检查是否已声明该对象：

var firstRun = firstRun || {ran: false};

if (firstRun.ran == true) {
    console.log("This is your first run");
    firstRun.ran = false;
} else {
    console.log("You have already run this loop at least once");
};