Asp.net 页面调用javascript变量的值

<td align="center" style="width: 183px; height: 25px"> 
纬度:<asp:TextBox ID="TextBox_l" runat="server" Width="76px"></asp:TextBox> 
经度:<asp:TextBox ID="TextBox_2" runat="server" Width="95px"></asp:TextBox> 
</td> 

<script> 
//赋值给页面变量 
document.getElementById("TextBox_l").value = "要赋给它的值"; 
document.getElementById("TextBox_2").value = "要赋给它的值"; 
</script>