AJAX request doesn't work in IE (url encoding problem)

The story

I have a simple mobile site, which makes Ajax requests to an external REST API. Some part of the application works, but others not. I noticed that the problematic requests contain JSON. I.e. something like:

/api/get/list?filter={"approved":1,"eventId":"4f86ca35fd33d9a55a000001"}&token=EC46FADECA4C

In Google Chrome, the actual request string looks like that:

/api/get/list?filter={%22approved%22:1,%22eventId%22:%224f86ca35fd33d9a55a000001%22}&token=EC46FADECA4C

The backend understand the query, parses it and returns a proper result. However, without correct url encoding the things are not working.

The solution

During the url preparation I replaced

url += JSON.stringify(parameter);

with

url += encodeURIComponent(JSON.stringify(parameter));

And the problem is fixed. Now even the crappy IE works.