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>