[jQuery] [BlockUI Plugin]use links instead of buttons

[efet]

At script's demo page, blockui's developer used buttons to activate
the scripts. How can I use links instead?

I tried it as below but it did not work.
<a href="javascript:void(0)" id="demo5">xxx</a>


html:
                <button id="demo5">Run</button>

js:
        $(document).ready(function() {

                $('#demo5').click(function() {
                        $.blockUI({
                                message: $('img#productimage'),
                                css: {
                                        top:  ($(window).height() - 500) /2 + 
'px',
                                        left: ($(window).width() - 500) /2 + 
'px',
                                        width: '500px'
                                }
                        });

                        setTimeout($.unblockUI, 2000);
                });

        });