This week I upgraded a web service project to v3.5 of the .Net framework.  However, another website then stopped working as it called the web service using JavaScript (by referencing the client-side proxy created by the Microsoft Ajax Library).  After a little bit of debugging I found that the response from a 3.5 webservice is different to a v2.0 service.  My webservice just returned a Guid.  When the service was using v2.0 the response just contained a guid.  Once it was upgraded to v3.5 however, it returned an JSON object with a property called ‘d’ and the value of ‘d’ was the guid.

How to fix

There are a couple of ways to get around this problem.  The easiest is probably to just upgrade the website to 3.5 as well, as then the serialisation of the object will be done for you automatically.  However, this wasn’t an option for me.  Instead I modified my JavaScript callback method to work with either response format.  The code changed from this:

function onCallback(result, context)
{
    var guid = result;
    //do further processing here...
}

to this:

function onCallback(result, context)
{
    var guid = result.d ? result.d : result;
    //do further processing here...
}

All we are doing is checking for the existence of the ‘d’ property and either getting the result from there or just using the result itself.  The benefit of this simple change is that the callback method will continue to work for any combination of v2.0 and v3.5 websites and services.

Hopefully this will be useful for somebody!  Posting it here so that I don’t forget about it myself in the future!