Moving selected listbox values to another listbox

<script type="text/javascript">
function MoveOption(objSourceElement, objTargetElement){ 
        if(objSourceElement.value==''){
                alert('Please select an option to move.')
                return false;   
        }       
        var aryTempSourceOptions = new Array();        
        var x = 0;               
        for (var i = 0; i < objSourceElement.length; i++){            
                if (objSourceElement.options[i].selected){              
                        var intTargetLen = objTargetElement.length++;                
                        objTargetElement.options[intTargetLen].text = objSourceElement.options[i].text;                
                        objTargetElement.options[intTargetLen].value = objSourceElement.options[i].value;            
                }else{                
                        var objTempValues = new Object();                
                        objTempValues.text = objSourceElement.options[i].text;                
                        objTempValues.value = objSourceElement.options[i].value;                
                        aryTempSourceOptions[x] = objTempValues;               
                        x++;           
                }       
        }              
        objSourceElement.length = aryTempSourceOptions.length;       
        for (var i = 0; i < aryTempSourceOptions.length; i++){            
                objSourceElement.options[i].text = aryTempSourceOptions[i].text;           
                objSourceElement.options[i].value = aryTempSourceOptions[i].value;           
                objSourceElement.options[i].selected = false;        
        }    
} 
 
function selectAll(){
	var optionList=document.getElementById('cat1').options;		
	var len = optionList.length; 
	for(i=0; i<len; i++){
		optionList.item(i).selected=true
	}
}
 
</script>
 
<input type="button" onClick="selectAll()" value="select all" >
<input type="button" onClick="document.getElementById('cat1').selectedIndex=-1;" value="deselect all" >
 
<select size="5" id="cat1" name="cat1" multiple>
    <option value="1">Value 1</option>
    <option value="2">Value 2</option>
    <option value="3">Value 3</option>
    <option value="4">Value 4</option>            
</select>
 
    <input type="button" onClick="MoveOption(document.getElementById('cat1'), document.getElementById('cat2'));" value=">">
   	
    
    <input type="button" onClick="MoveOption(document.getElementById('cat2'), document.getElementById('cat1'));" value="<">
 
<select size="5" id="cat2" name="cat2" multiple>
             
</select>

                                              

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