Hi,
fetchData routine make an ajax request, passes along jsonDataM to the
handler routine, at which time the responseJSON result is assigned to the
json parameter.
Remember that it's the *value* of `jsonDataM` that gets bound to the
function, not a reference to the variable. (JavaScript is purely pass-
by-value; the value passed in the case of object references is a
reference to the object, but it's still just a value being passed.) So
if your handler function inside `fetchData` is ending up doing
something like this:
jsonData = response.responseJSON;
...that's not going to have any effect on `jsonDataM`. All you're
doing there is assigning the value of the `responseJSON` property to
your local argument variable within `fetchData`. It's exactly like
doing this:
var foo = 5;
bar(foo);
alert(foo);
function bar(f) {
f = 6;
}
The alert will still show 5, not 6. Assigning to `f` doesn't have
any effect on `foo`.
One obvious answer is to have `fetchData` just assign directly to
`jsonDataM`, since it's a global, but I hate to offer an answer
suggesting using global variables (even if you already have them), and
I'm guessing you have a reason for making the destination for the data
an argument you give to `fetchData`.
It's easy to simulate pass-by-reference in JavaScript using object
properties. Instead of having a `jsonDataM` variable, have a variable
that's an object containing a *property* called `jsonDataM`. Pass that
object's reference to `fetchData`, and have `fetchData` write to its
`jsonDataM` property.
Applying that solution to my example above:
var obj = {
foo: 5
};
bar(obj);
alert(obj.foo);
function bar(o) {
o.foo = 6;
}
Now it alerts 6.
If I'm completely off-base on the above, first off: Apologies. And
second off: My next guess is that the code isn't handling the fact
that the ajax request is *asynchronous*. But my first guess (since
you've titled this as a question about variable scope) is that it's
the pass-by-value thing.
HTH,
--
T.J. Crowder
Independent Software Engineer
tj / crowder software / com
www / crowder software / com
On Apr 16, 11:18 pm, kstubs kst...@gmail.com wrote:
In the following, assuming jsonDataM is defined top of my script (so scope
of this variable should be good):
mapqueryform.observe('submit', fetchData.bindAsEventListener(mapqueryform,
jsonDataM));
fetchData routine make an ajax request, passes along jsonDataM to the
handler routine, at which time the responseJSON result is assigned to the
json parameter. I'm expecting my global jsonDataM to have valid json data,
but it is just NULL.
To be clear, here is the function definitions for fetchData and the handler:
function fetchData(e, jsonData) { ... }
function handleFetch(response, jsonData) { ... }
and in fetchData, here is the onComplete:
onComplete: function(response) { handleFetch(response, jsonData); }
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