Mac,
What you're doing is kind-of impossible to accomplish using straightforward means. When you use the code you've included in the question, you're actually removing the visibility of the entire box, not just the text content.
Some ideas:
- Make the textcolor the same as the background color.
- Use the onKeyPress event, after every keystroke take the value from this box, and append it into a hidden textbox you've got elsewhere on the page (or a javascript variable.
Combining these should be pretty effective in what you're tryin to do.
More important is the question: Why would you want to do this? Could you elaborate on what it is you're trying to accomplish here?
Edit: I see you're doing this for passwords. In that case, why not use the <input type="password"> field? That way the browser know it's a password field and hides the input automatically (using the standard dots, or stars).