really great; just needs 1 tweak

this works exactly as described. it would be even better if the content of the [qrcode] shortcode could be another shortcode, e.g.

[qrcode][field url][\qrcode]

Heres the PHP that’ll make it do that:

function qrcode( $atts, $content = null ) {
    return '<div id="qrcode"></div>
<script type="text/javascript">
new QRCode(document.getElementById("qrcode"), "'.do_shortcode($content).'");
</script>';
}

add_shortcode("qrcode", "qrcode");