Question

I have an ASP.NET form (C#) but which I click this button that should execute a JS method I get the error “Microsoft JScript runtime error: ‘document.getElementById(…)’ is null or not an object”

This is odd because it should work:

                <asp:LinkButton ID="btnDriverPopulate" runat="server" Text="" Height="55px" Width="172px" CssClass="btnMTO" 
                    OnClientClick="readLicense()" ToolTip="Check Driver" /> 

textbox code here

 <asp:TextBox ID="DriverLast" runat="server" Width="180px" Text='<%# Eval("Last") %>' ToolTip="Enter driver last name"></asp:TextBox>
                                    <cc:TextBoxValidator ID="valDriverLast" runat="server" AllowBlank="false" Display="dynamic" ControlToValidate="DriverLast" ValidationGroup="ValGrpDriver"
                                        CorrectFormat="Please enter in alphanumeric characters only." FieldName="Last Name" RegString="^[a-zA-Z0-9\s.,\-']+$" />

JS function readLicense that SHOULD set the textbox’s value to “hi”

document.getElementById("DriverLast").value = "hi";

Answer 1

The rendered client id isn’t necessarily the same as the server control id. You can use the ClientIDMode property to change this behavior.

document.getElementById("<%= DriverLast.ClientID %>").value = "hi";