可变提升 - “var”在函数中使用全局变量名称 [英] Variable hoisting - "var" with global variable name in function

问题描述

我正在练习一些场景并找到一个案例：

I was practicing some scenario and find a case:

这里是小提琴

根据关闭栏功能应该可以访问 var x 所以我由于 if（！1），预计会发出警报1并且条件变为假，但它会提醒 undefined 并且条件变为真，第二个警报值为10.

According to closure bar function should have access to var x so I expected to alert 1 and condition get false due to if(!1) but it alerted undefined and condition get true and second alert is with value 10.

var x = 1;
function bar() {
    alert(x);
    if (!x) {
        var x = 10;
    }
    alert(x);
}
bar();

所以我很困惑为什么它会提示未定义？

So I am confused why it is prompting undefined?

根据特定范围内的提升，您可以在任何位置始终定义变量。

According to hoisting in a particular scope you define a variable anywhere it is considered as defined at top always.

如果是由于提升效应，它仍然需要提醒10而不是未定义。

If it is due to hoisting effect it still have to alert 10 instead of undefined.

推荐答案

提升将使您的代码有效工作像这样：

Hoisting will make your code effectively work like this:

var x;
x = 1;
function bar() {
    var x; //same as var x = undefined;
    alert(x);
    if (!x) {
        x = 10;
    }
    alert(x);
}
bar();

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