Setting hidden input value in Javascript, then accessing it in codebehind

I have been trying to set the value of a hidden input by using Javascript and then access the value from within my C# codebehind. When I run the code that is copied below, the value that is assigned to assignedIDs is “”, which I assume is the default value for a hidden input. If I manually set the value in the html tag, then assignedIDs is set to that value.

How to remove flashing on persisting remotely populated jqgrid tree node

jqGrid tree nodes are read from server using json data. Click in node reads child nodes from server.
Code below is used to restore opened tree node if page is loaded.
Only single node is opened always in tree.
Controller assings node ids to autoClicked array and gridComplete opens nodes using this path.
This causes grid flasinging on page load since multiple server requests buid grid multiple times.
How to disable grid flashing ?
Is it possible to prevent multiple jqGrid building and show only find jqGrid tree ?

Calling server side event in asp.net from java script

Surely will be marked as duplicate one but after tons of question and example i couldn’t solve my problem.

What i want?
Calling server side event handler in asp.net from client side java script it is not going on server side. I checked it by setting breakpoint, the page flicks but server side method is not called.

My click event on code behind is