Set asp.net textbox value using javascript

Question

I want to set the value of a asp.net textbox using javascript

My JS Code is:

document.getElementById('<%=txtFlag.ClientID %>').value = "Track";

My textbox is:

<asp:TextBox ID="txtFlag" runat="server" Visible="False"></asp:TextBox>

But it gives me an error document.getElementById(...)' is null or not an object

I dont understand what is wrong.

Please help.

Answer 1

<asp:TextBox ID="txtFlag" runat="server" Visible="False"></asp:TextBox>

Setting visible=false will cause this textbox to not appear in the rendered page. Remove this, and add display:none;

<asp:TextBox ID="txtFlag" runat="server" style="display:none;"></asp:TextBox>