javascript - Proper for/in variable declaration -

Reasonable to declare the loop-specific variable in What is the syntax? / in loop?

The first two work both (and do not raise any flag in Google Claus compiler), but only the third person crosses the JC of Crockford, a type of tree. I am reluctant to use it, mostly because it is not compact.

JSLint complains that either val is a bad variable (when I use var ), or the declaration should be transferred.

What are the drawbacks for the first or the second option? What should I use? (Example assumes that str is a declared string and vals is a declared object)

1 no announcement:

 For  (Val in Wall) {if (vals.hasOwnProperty (val)) {str + = val; }}   
 for different announcements:  
  (var val in vals) {if (vals.hasOwnProperty (val)) { Str = val; }}   
 Out of 3 Loop Wars announcements:  
  var val; For (Val in Wall) {if (vals.hasOwnProperty (val)) {str + = val; }}    
 
 
 Feel free to ignore JSLint. It's more guideline than anything 2 and 3 are functionally similar, either (I use 2) feel free to use. For the first time a global 'val' variable is disclosed, do not do so :)  
 The reason behind the FII third argument is that inline variable delivery is more difficult than spot / search:  
  var a, b, c, d, e;   
 At the top of the function.