wait for ajax based elements to load - C# - IJavaScriptExecutor

I have a  bit of difficulties with using following command to detect when jquery code in  the code I am testing has been completed:

bool ajaxIsComplete = (bool)jsDriver.ExecuteScript("return jQuery.active == 0");

You can see I am using C#. So here that is defined as part of Seleneim 2.X:


IJavaScriptExecutor



So the problem is:



ClassSelProgram.waitForAjax(15);



IWebElement ClickButton = firefox.FindElement(By.CssSelector("td.BoxHeadCell:nth-child(21) > input"));



                   

ClickButton.click();



That tree instruction works for  some cases but do not for others. I am testing mixture of MVC and jquery. So I have to know the exact time when  jqery is completed. So in many places on the  is suggested:

checking return jQuery.active == 0






But I do not know  why is that? Or maybe I might have my own small javascript to test that on my own. Any suggestions?