Summary of various ways in which javascript removes the option option

var oSel=document.form1.DropDownCity; 
while(oSel.options.length>0){ 
oSel.removeChild(oSel.options[0]); 
} 

<SCRIPT LANGUAGE="JavaScript"> 
function del1(){ 
var obj = document.getElementById("s"); 
var count = obj.options.length; 
for(var i = 0;i<count;i++){ 
obj.options.remove(0);//Each time I delete the index, I get 0
} 
} 
</SCRIPT> 

<script language="javascript"> 
function del() { 
for (var i = s.options.length - 1; i >= 0; i --) 
s.options[i] = null; 
} 
</script> 

<SCRIPT LANGUAGE="JavaScript"> 
function del1(){ 
var obj = document.getElementById("s"); 
obj.options.length=0 
} 
</SCRIPT> 

function removeOption(index)   
{    
    document.getElementById("selUnassignedUsers").options.remove(index);    
}   

function removeOption(index)    
{    
    document.getElementById("selUnassignedUsers").remove(index);    
}