HTML, 36 30 19 bytes

<noscript>0<script>

Saved a 17 bytes, thanks to DeepSeek for shrinking my code!

Please note this code won't follow correct HTML syntax, however at least it worked... It will show you a '0' character when JavaScript disabled, showing nothing when JavaScript is enabled.

The old 30-character code:

<noscript>N</noscript><script>

The very old 36-character code:

<p id=a>N<script>a.remove()</script>