[thelist] DHTML questions...

[JTocher]

Jeff, thanks muchly for the clarification on variable scope - it's starting
to sink in. I've been trying to get my mind around how how variables work
within functions and had not found a clear explanation when reading through
various tutorials. Yours did the trick!

Txs...
Janice


on 11/16/01 3:00 AM, you wrote:

> chris,
> 
>> <><><><><><><><><><><><><><><><><><><><><><><><><><><><><
>> From: The Optimizer
>> 
>>> function locateBox(top_loc,left_loc)
>>> {
>>> return top_loc;
>>> return left_loc;
>>> }
>> 
>> First point, you need to understand variable scope.
>> These are local variables, their scope being within
>> the function only.
>> <><><><><><><><><><><><><><><><><><><><><><><><><><><><><
> 
> actually they're neither local or global.  they're statements that are being
> returned to the calling object or event handler.  technically only the first
> one is being returned because execution of a return statement halts further
> execution of the function.
> 
> i'll describe briefly how variable scoping works in javascript so everyone
> understands.  when creating variables they are global by default, unless you
> specify otherwise.  in order to create a local variable, you must use the
> var keyword within the function.
> 
> think of a function like a box with holes in its walls for every variable
> inside and outside the function.  now, every time you refer to these
> variables either to read or write them, it reaches outside the box through
> one of these holes to access them.  if you define a variable inside the
> function as a local variable (using the var keyword), it doesn't create a
> hole for it to the outside or if a variable by the same name already exists
> outside the function it closes the hole off for that variable.  this has a
> couple of side-effects.
> 
> 1)  if there _is not_ a variable by the same name
> defined outside the function, then trying to
> access a variable by that name outside the
> function will result in an error.
> 
> here's an example:
> 
> <script language="JavaScript" type="text/javascript">
> <!--
> function myFunc()
> {
> var myVar = 'foo';
> }
> 
> alert(myVar);
> // -->
> </script>
> 
> run this function and you'll get an error "myVar is undefined".
> 
> 2)  if there _is_ a variable by the same name
> defined outside the function, then setting the
> value of the variable within the function will
> not change the value of the variable outside
> the function.  in fact, it's impossible to read
> or write the variable outside the function as
> defining the variable of the same name within
> the function makes the variable outside the
> function invisible.
> 
> <script language="JavaScript" type="text/javascript">
> <!--
> var myVar = 'foo';
> 
> function myFunc()
> {
> alert(myVar);
> var myVar = 'bar';
> alert(myVar);
> }
> 
> alert(myVar);
> 
> myFunc();
> 
> alert(myVar);
> // -->
> </script>
> 
> the 1st alert dialog will contain the value "foo".  the 2nd (the 1st one
> inside the function "myFunc()") will contain the value "foo" because the
> local variable has not been defined yet so the function can access the
> global variable.  the 3rd (the 2nd one inside the function "myFunc()") will
> contain a value of "bar" because the defining of the local variable
> overwrites the global variable within the function.  the 4th and final one
> will contain the value "foo" once again as the global variable value still
> has not been changed.
> 
> i hope this makes variable scoping alittle more clear for someone.
> 
> thanks,
> 
> ..jeff
> 
> http://evolt.org/
> jeff at members.evolt.org
> http://members.evolt.org/jeff/
> 
> 
> 
> 
> 
> ---------------------------------------
> For unsubscribe and other options, including
> the Tip Harvester and archive of TheList go to:
> http://lists.evolt.org Workers of the Web, evolt !