Spoiler in java question (bbcode)

[Tri@de]

If i make a bbcode with this:

-----------------
<script type="text/javascript">

function showSpoiler(block) {

block.nextSibling.nextSibling.style.display ="block";
block.parentNode.removeChild(block);
}
</script>

<input type="button" class="button" onClick="showSpoiler(this);" value="Mostra Spoiler">
<span class="content" style="display:none">ciao</span>
----------------------

is dangerous for my forum?
i heard that javascript bbcode could suffer of hacker attack.

It's true?

Someone can answer me?