问题描述
考虑以下代码:
<html><head></head>
<body>
<script type="text/javascript">
var outside_scope = "outside scope";
function f1() {
alert(outside_scope) ;
}
f1();
</script>
</body>
</html>
此代码的输出是警告框显示消息outside范围".但是，如果我将代码稍微修改为:
The output for this code is that the alert box displays the message "outsidescope". But, if I slightly modify the code as:
<html><head></head>
<body>
<script type="text/javascript">
var outside_scope = "outside scope";
function f1() {
alert(outside_scope) ;
var outside_scope = "inside scope";
}
f1();
</script>
</body>
</html>
警报框显示消息未定义".我本可以有如果在两种情况下都显示未定义"，则理解逻辑.但是，那个没有发生.它仅在第二种情况下显示未定义".这是为什么?
the alert box displays the message "undefined". I could haveunderstood the logic if it displays "undefined" in both the cases. But, thatis not happening. It displays "undefined" only in the second case. Why is this?
预先感谢您的帮助！
推荐答案
在第一种情况下，您的代码正在访问全局变量outside_scope"，该变量已被初始化为outside scope".
In the first case, your code is accessing the global variable "outside_scope", which has been initialized to "outside scope".
Javascript 具有函数级作用域，因此在第二种情况下，它访问的是函数作用域变量outside_scope"，但在出现警告框时尚未初始化.所以它显示未定义.
Javascript has function level scope, so in the second case it is accessing the function scoped variable "outside_scope", but it has not yet been initialized at the time of the alert box. So it displays undefined.
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