[Javascript] global vars prob?!

[Nick Fitzsimons]

Michael Borchers wrote:
> i dynamically create a textarea in a for() like this:
>  
> var offersNumRows = 2
>  
> var offersNumRowsAdded=4 (f.e.)
>  
>  for(o=0;o<offersNumRowsAdded;o++)
>  { 
> 
>       var numRow = offersNumRows + o;

<snip>

>     HERE COMES THE TROUBLE MAKER:
>   inputProductsDescription.onfocus=function() { 
> products_price_return(numRow); }; 
>  
> ...
>  
> }
>  
> => NUMROW FINALLY IS 6
>  

When you refer to numRow in the event handler function, you create a 
closure, meaning that the function has a reference to the variable 
numRow - the "box" labelled "numRow", if you will. Note that this is not 
the same as having a reference to the _value_ that the variable contains 
at the time the closure is created; when, at a later time, the event 
handler executes, it will look at the variable and find it contains the 
value 6, because that is the value left there when the loop had finished 
executing.To get a feel for this, add a line after your loop that sets 
numRow to (say) 23; 23 is then the value the event handler will see in 
there when it executes.

One way to achieve the effect you're looking for is to move the event 
handler assignment into a function:

function assignFocusHandler(element, rowNumber) {
	element.onfocus = function() {
		products_price_return(rowNumber);
	};
}

Invoke this in your loop using

assignFocusHandler(inputProductsDescription, numRows);

When the function executes, the event handler will form a closure over 
the parameter rowNumber, which is a different instance of the parameter 
for each invocation of the function, each instance therefore (in this 
case) having a different value; and you'll get the effect you wanted.

(Of course, for consistency, you may want to call the parameter "numRow" 
rather than "rowNumber"; I just chose a different name to emphasise that 
within the function, it's a different "box" to the one in the calling 
function, and contains a _copy_ of the value stored in numRow.)

HTH,

Nick.
-- 
Nick Fitzsimons
http://www.nickfitz.co.uk/