switch / case语句中的JavaScript变量范围是什么？ [英] What is the JavaScript variable scope in a switch / case statement?

问题描述

在使用ASP.NET MVC创建JavaScript时，我注意到了几个范围警告，并意识到我在切换/ case语句中理解变量范围时遗漏了一些东西。

While creating JavaScript with ASP.NET MVC I noticed several scope warnings and realized that I am missing something with understanding the variable scope inside the switch / case statement.

警告：'i'已定义引用案例b和案例c

Warning: 'i' is already defined referring to case b and case c

我的代码与此类似：

switch(element) {
  case 'a':
   for(var i=0; i < count; i++){
    do something
   }
   break;

  case 'b':
   for(var i=0; i < count; i++){
    do something
   }
   break;

  case 'c':
   for(var i=0; i < count; i++){
    do something
   }
   break;
}

我认为范围以每个break语句结束，但似乎范围没有结束直到开关/外壳结束。是整个开关/案例的范围吗？

I thought scope ended with each break statement but it seems that scope does not end until the end of the switch/case. Is scope for the entire switch/case?

推荐答案

Javascript不使用块范围。

Javascript does not use block scope.

因此，所有局部变量都在声明它们的整个函数的范围内。

Therefore, all local variables are in scope throughout the entire function in which they were declared.

但是，在您的特定情况下，没有C类似语言（我知道），其中每个 case 语句形成一个独立的范围。

例如，以下C＃代码将无法编译：

However, in your particular case, there is no C-like language (that I know of) in which each case statement forms an independent scope.
For example, the following C# code will not compile:

switch(someVar) {
    case 1:
        int a;
        break;
    case 2:
        int a;        //'a' is already defined
        break;
}

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