How to pass data between C# and Javascript in Windows Phone 8.1 App

I've a webview in my Windows Phone 8.1 app where I run javascript code that calls a C# method and the C# method returns some string data. I need this string data in the javascript code from where the C# method was called previously. How can I do this data passing operation in Windows Phone 8.1 app?

To be more specific, I've following snippet in javascript:

var code = DownloadProblemTast.getProblemBody(i);

DownloadProblemTast is a class in C# and getProblemBody(i) is a method inside it.

As far I know, I can call the C# method with window.external.notify() from the javascript side, but how can I receive the data sent by the C# method that is just called.