Call javascript function?

hello everybody

I put this javascript in me new blog

<script language="javascript" type="text/javascript">
function showAlert() {
 alert('Hello World - this is an alert message!');

and wanna call it anywhere not inside the blog using flash

for example : I wanna make a flash and embed it to any website
in this flash a button with geturl to call that function

I did this but it failed :

btn.onRelease = function () { 
getURL('javascript:baseURL("") & showAlert()')

please help me