Disable backspace in textbox via javascript

Question

I have a textbox which is extended by an Ajax Control Toolkit calendar.

I want to make it so that the user cannot edit the textbox and will have to instead use the calendar extender for input.

I have managed to block all keys except backspace!

This is what I have so far:

<asp:TextBox ID="TextBox1" runat="server" onKeyPress="javascript: return false;" onKeyDown="javascript: return false;" onPaste="javascript: return false;" />

How would I also disable backspace within the textbox using javascript?

EDIT

Made an edit since I need a solution in javascript.

EDIT

It turns out that onKeyDown="javascript: return false;" DOES work. I have no idea why it wasn't working before. I tried using a new textbox and it blocked backspaces fine. So sorry to everyone who posted an answer hoping to get some rep esp. after I marked it for bounty.

My textboxes now (seem) to block ALL keystrokes and also still work with the calendar extender.

Answer 1

ZX12R was close. This is the correct solution:

The TextBox is like this:

    <asp:TextBox ID="TextBox1" runat="server" onKeyDown="preventBackspace();"></asp:TextBox>

and the script looks like this:

<script type="text/javascript">
    function preventBackspace(e) {
        var evt = e || window.event;
        if (evt) {
            var keyCode = evt.charCode || evt.keyCode;
            if (keyCode === 8) {
                if (evt.preventDefault) {
                    evt.preventDefault();
                } else {
                    evt.returnValue = false;
                }
            }
        }
    }
</script>

First of all, the backspace wont come through on Key Press, so you have to use Key Down.