actionscript-3 - 在循环之外定义变量更好吗？

Question

第二个比第一个好？

第一个:

var count:int=myArray.length;
for(var i:uint=0;i<count;i++)
{
   var str:String=myArray[i].label;
   var somethingElse:Class=...;
   var andAnotherThing:MyInstance=new MyInstance(somethingElse);
   ...
}

第二:

var count:int=myArray.length;
var str:String;
var somethingElse:Class;
var andAnotherThing:MyInstance;
for(var i:uint=0;i<count;i++)
{
   str=myArray[i].label;
   somethingElse=...;
   andAnotherThing=new MyInstance(somethingElse);
   ...
}

谢谢你。

Answer 1

在 Actionscript 和 Javascript 中，变量的作用域是函数，而不是块。这称为变量提升。

ActionScript 3.0 Variables

An interesting implication of the lack of block-level scope is that you can read or write to a variable before it is declared, as long as it is declared before the function ends. This is because of a technique called hoisting , which means that the compiler moves all variable declarations to the top of the function.

无论您在函数中的何处声明变量，您的代码都会如此有效地表现如下:

var count:int;
var str:String;
var i:uint;
var somethingElse:Class;
var andAnotherThing:MyInstance;

count = myArray.length;
for(i=0;i<count;i++)
{
   str=myArray[i].label;
   somethingElse = ...;
   andAnotherThing = new MyInstance(somethingElse);
   ...
}

尽管如此，我仍然更喜欢在使用它们的块中声明我的变量，主要是出于维护原因和一般性的清晰度。