Is it better to define vars outside of loops?

Question

Is the second better than the first?

FIRST:

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);
   ...
}

SECOND:

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);
   ...
}

Thank you.

Answer 1

In Actionscript and Javascript, variables are scoped to the function, not the block. It's called variable hoisting.

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.

So effectively your code will behave like this regardless of where you declare your variables within the function:

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);
   ...
}

Nevertheless, I still prefer to declare my variables within the blocks that use them primarily for maintenance reasons and general clarity.

Answer 2

On Flash, the answer is it doesn't matter. Flash is weird when it comes to variable declaration. Do the following and see what happens:

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

Even though str ran out of scope out of the for loop, you will get a variable redefinition warning, meaning that the variable will only be "initialized" once in a for loop;