client side data lose when posback occurs in asp.net c#

Question

 have 10 list boxes in my for all 10 list boxes same function is using for some buttons i want to add listbox data to grid can you help me  my java script code shown below

<script language="javascript" type="text/javascript" >

    function MoveItem(ctrlSource, ctrlTarget) {

       var Source = document.getElementById(ctrlSource);

       var Target = document.getElementById(ctrlTarget);



       if ((Source != null) && (Target != null)) {

           while ( Source.options.selectedIndex >= 0 ) {

               var newOption = new Option(); // Create a new instance of ListItem

               newOption.text = Source.options[Source.options.selectedIndex].text;

               newOption.value = Source.options[Source.options.selectedIndex].value;

               

               Target.options[Target.length] = newOption; //Append the item in Target

               Source.remove(Source.options.selectedIndex);  //Remove the item from Source

           }

       }

i tried a javascript above code to move items between listbox using html input button problem when i trying to save listbox.items.count giving 0 can anyone tell me why this happening and also when post back occurs listbox items lost.