在Javascript中设置隐藏的输入值，然后在代码隐藏中访问它

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.I have been trying to set the value of a hidden