Note details: Variable scopes in Javascript

Let's take a look at the Javascript script code: 1 <script language = "JavaScript">
2 <! --
3 var v = "AAA ";
4 function func ()
5 {
6 alert (v );
7 var v = "BBB ";
8}
9 // -->
10 </SCRIPT>

What is alert? In our opinion, it should be "AAA". In fact, what alert comes out is "undefined ". Why?
To simplify processing, JavaScript only has two scopes: global variables and internal variables of functions. The scope of the variables defined in any part of the function is the whole function body. At the time of alert, the internal variable V of the function has been defined, and the global variable definition with the same name has been overwritten, but it has not been initialized yet. Therefore, alert came out with "undefined ".