js object is created like this:
var myobject = { prop1: 'hello',
prop2: function(){//whatever},
prop3:'yay'};
myobject.prop1; //'hello'
myobject.prop2(); //that's right, it runs that function(){//whatever} in prop2
You cannot access any server side methods with JS directly. Make an AJAX request with a JSON object, parse it in ASP.NET, and in ASP.NET, call your function you want based on what it says in the object.
Flash can use ExternalInterface.addCallback to do a direct JS access but I am not sure ASP.NET has such a thing (and I would strongly recommend against using a "Flash's blackbox JS access" style anyway).
If you already added a JS object to your user control somehow server side by executing javascript, you just access it like this:
myUserControlAssociatedJSObject.myFunction(); //it runs it!