Access Dropdown Menu's Variable In Java Script On Change Event

I want to access drop down menu's variable in java script on change event, here is my code

<asp:DropDownList ID="DropDownList1" runat="server" onchange="document.location.href = url_Lookbook;" >
<asp:ListItem Value="0">hello</asp:ListItem>
<asp:ListItem Value="1">world</asp:ListItem>
</asp:DropDownList>

here is the script coding:

<script type="text/javascript">
var url_Lookbook = "http://microsoft.com";
</script>

My question is how do I pass down value=0 or value = 1 to different page