Calling Javascript function from code behind

  <asp:TextBox ID="TextBox1" runat="server"  AutoPostBack="true" OnTextChanged="Click"></asp:TextBox>

  <script type="text/javascript" language="javascript">     
       function validate(msg) {
            var text1 = document.getElementById("divtext");
            if (msg == "y") 
            {
                text1.style.color = 'Green';
            }
            else
             {
                text1.style.color = 'Red';
            }
              }
        </script>

 protected void Click(object sender, EventArgs e)
    {
        string msg = TextBox1.Text.Trim();
        string fun = "validate('" + msg + "')";
        ScriptManager.RegisterStartupScript(Page, typeof(Page), "Validate", fun, true);
    }