How to call Web Service synchronously

I have created ASP.NET Web Service, generated client proxy script using Script Manager. Now I can successfully

call Web Service method from jscript.
function onClick()
{
var proxy = GridDemo.employee_controller.ListEmployees(onSuccess, onFailure);
}

 
function onSuccess(sender, e)
{

alert(sender);
}
 
function onFailure(sender, e)
{
alert("Problem retrieving web service data");
} Go to the complete details ...