Calling javascript object method using WebBrowser.Document.InvokeScript

In my WinForms application I need to call javascript function from my WebBrowser control. I used Document.InvokeScript and it works perfect with functions alone e.g

Document.InvokeScript("function").

But when i want to call javascript object method e.g.

Document.InvokeScript("obj.method")

it doesn't work. Is there a way to make it work? Or different solution to this problem? Without changing anything in the javascript code!

Thanks in advance :)