Move <option> to top of list with Javascript

I'm trying to create a b开发者_如何学运维utton that will move the currently selected OPTION in a SELECT MULTIPLE list to the top of that list. I currently have OptionTransfer.js implemented, which is allowing me to move items up and down the list. I want to add a new function

function moveOptionTop(obj){ 
var i = obj.selectedIndex; 
if(i == 0){return;} 
var length = obj.options.length; 
for(j=length;j>0;j++){ obj.options[j] = obj.options[j-1]; //move all elements up a position to free up index 0 } 
obj.options[0] = obj.options[i+1]; //set new [0] element
for(j=i+1;j

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Use DOM manipulation methods. Given:

var select = document.getElementById ("...");     // select element
var option = select.options[select.selectedIndex] // option element

1. Remove selected option from select: select.removeChild (option)
2. Reinsert it as first child: select.insertChild (option, select.firstChild)

Or use select.add() and select.remove()

http://www.w3schools.com/jsref/dom_obj_select.asp