Node-soap client and scope of the callback

Question

Node-soap client and scope of the callback

I'm using the node-soap client from milewise (create API by the way), but I have some difficulties to get the results of the callback to the right scope.

Here is the code I have for now:

function generateSoapRequest(req, res, next)
{ 
    soap.createClient('http://127.0.0.1:' + cfg.service_port + cfg.service_url_path,
    function(err, client) {
        client.CXIf.CXIf.CXProcessXML(
            {"XMLRequestData": {"CXLogon": {"UserID":"1901007", "Password":"2580", "LogonType":11 } } }, 
            function(err, result, body) {
            if (err) {
                console.log(err);
                return;
            }
            console.log(result);

            var cxresponse = result.XMLResponse[0].CXResponse;
            console.log('SessionID:' + cxresponse.SessionID + ' SessionInstanceID:' + cxresponse.SessionInstanceID);
        });
    });
}

function getVoiceMailInformation(req, res, next) {
    var cxresponse = generateSoapRequest(req, res, next);
    var something = doSomethingNext(cxresponse);
}

function doSomethingNext(cxresponse){....; return something;}

Basically, when I launch the getVoiceMailInformation(), it creates a soap client and request some information through the generateSoapRequest(). The next step would be to get the result of that function (not implemented in the code above, because I don't know how) and do something else.

My problem is soap.createClient is asynchronous, so the callback is fired well after the function is complete.

What would be the best approach ? (Maybe it's something trivial, but the scope of an anonymous function in javascript is something that is killing me.)

Any help will be very appreciated.

node.js
soap
asynchronous
callback

Answer 1

Basically you can't do something like:

var cxresponse = generateSoapRequest(req, res, next);

because the function you're calling invokes asynchronous code, and therefore can't return a value that's determined by that code. The normal way around this is to give the function an extra callback parameter for a function that will be called with the result once the result becomes available. It doesn't have to be an anonymous function; it can be a named function. In your case, (assuming you've modified generateSoapRequest to take a callback as its fourth argument and call it when the results are ready, you could write

generateSoapRequest(req, res, next, doSomethingNext);

and then doSomethingNext will be called with cxresponse as an argument. Of course, since doSomethingNext also gets called asynchronously, it can't return a value either, so you'll have to apply the same technique to it.

The async module can make this sort of thing easier: in particular, its "waterfall" pattern is useful when you have a bunch of functions that have to run in sequence, each being called back from the previous one.