Small javascript question

I'am using a function:
<script type="text/javascript">
function welcome(x)
{
document.write(x);
}
</script>

Where it displays a text.

Now to set what the variable x is, I want to have it on an onclick event like:
<a href="#" onclick="welcome('Welcome to the site')">Click for welcome 1</a>
<a href="#" onclick="welcome('Hello!')">Click for welcome 2</a>

But the onclick codes do not work.

What should I do to correct this code?