Javascript function not returning properly?

Question

function IsSwap()
    {
        var urlString = "<%= System.Web.VirtualPathUtility.ToAbsolute("~/mvc/Indications.cfc/GetModelType")%>";
        var id = 
            {
                id : GetGUIDValue()
            }
            $.ajax({
                type: "POST",
                url: urlString,
                data: id,
                success: function(data) {
                    if (data.toString() == 'SwapModel')
                    {
                        return true;
                    }
                }
            });

Expected result is true. I can alert right before the return so I know it's getting to that point fine. In another function, I tried to get my bool and use it like this:

var isSwap = IsSwap();
            if (isSwap)

and it keeps saying isSwap is undefined. Why?

IS isSwap defined? Are you calling the function before it has been initialized? — josh.trow
– josh.trow, Commented Feb 28, 2011 at 16:04
at a first glance, you need to escape those double quotes in the urlString variable — Kyle
– Kyle, Commented Feb 28, 2011 at 16:05
the function or the variable? the function is being called fine yes. I can place an alert right before the return statement and see it popup when it needs to. Something is changing "true" to undefined on the call though when I assign it to the variable isSwap. — slandau
– slandau, Commented Feb 28, 2011 at 16:05
@Kyle -- it calls fine though. Goes through the controller, back onto the client side, and sets the return to true. For some reason the variable is being assigned true in the call to the function though. — slandau
– slandau, Commented Feb 28, 2011 at 16:06
IsSwap does not return a value, so the function returns undefined. The return true is from the Ajax success callback, not IsSwap. — Jonathon Faust
– Jonathon Faust, Commented Feb 28, 2011 at 16:07

SadullahCeran · Accepted Answer · 2011-02-28 16:07:41Z

You are using ajax requests, which are asynchronous. You can't return value from an ajax request. Try this instead:

function IsSwap()
    {
        var urlString = "<%= System.Web.VirtualPathUtility.ToAbsolute("~/mvc/Indications.cfc/GetModelType")%>";
        var id = 
            {
                id : GetGUIDValue()
            }
            $.ajax({
                type: "POST",
                url: urlString,
                data: id,
                success: function(data) {
                    if (data.toString() == 'SwapModel')
                    {
                        ResultIsTrue(); // call another function.
                    }
                }
            });

After execution, instead of using this:

var isSwap = IsSwap();
if (isSwap){
 // Do Somethinh
}

Try that:

IsSwap();
function ResultIsTrue(){
 // Do Same Thing
}

Richard Dalton · Accepted Answer · 2011-02-28 16:07:07Z

3

You can't return from an ajax call like that.

Essentially what you're doing is returning true from the inner function.

You should just call whatever code you need in the success method as that's the only time you can guarantee that the ajax call has completed.

answered Feb 28, 2011 at 16:07

Richard Dalton

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3 Comments

Richard Dalton Over a year ago

You still couldnt return it directly, but you could create a local variable inside the IsSwap function, set that on success and then return that.

Jonathon Faust Over a year ago

@slandau no, it won't. IsSwap does not return a value, so you get an undefined return value by default.

johnhunter Over a year ago

You should put the required logic within the success: function(data) fn. If that isn't possible you could pass a calback function to IsSwap which gets called on success.

Dan S · Accepted Answer · 2011-02-28 16:15:46Z

0

The AJAX request is asynchronous, meaning that IsSwap will return before the response to the AJAX request.

Whatever you need to do based on isSwap, you should do in the success handler of your AJAX request.

UPDATE: This last paragraph is incorrect about it working, but worth noting about synchronous not being recommended:

Alternatively, you could make the AJAX request synchronous (by adding async:false to the AJAX options) and keep it how you have it - however I wouldn't recommend this as your browser will 'freeze' whilst it waits for the response.

edited Feb 28, 2011 at 16:15

answered Feb 28, 2011 at 16:08

Dan S

8456 silver badges7 bronze badges

1 Comment

Jonathon Faust Over a year ago

It doesn't matter whether it's synchronous, he's not returning a value from IsSwap.

josh.trow · Accepted Answer · 2011-02-28 16:06:51Z

-2

Check this line:

var urlString = "<%= System.Web.VirtualPathUtility.ToAbsolute("~/mvc/Indications.cfc/GetModelType")%>";

Try using single quotes like so:

var urlString = '<%= System.Web.VirtualPathUtility.ToAbsolute("~/mvc/Indications.cfc/GetModelType")%>';

Your double quotes inside double quotes is most likely your problem.

answered Feb 28, 2011 at 16:06

josh.trow

4,90123 silver badges31 bronze badges

2 Comments

slandau Over a year ago

It makes the controller call absolutely fine though and gets to the last return statement.

johnhunter Over a year ago

-1 The string is fine. The problem is that an Ajax call is async so the logic needs to be in the success handler function.

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