Need help with javascript popup?

Hi there could somebody help me out with this bit of javascript?

<a href="javascript:;" onclick="document.forms[0].a_answer.value=document.forms[0].a_answer.value+'[link=PUT LINK HERE][/link]'">
Link Here
</a>

<form id="form1" name="form1" method="post">
<textarea name="a_answer" cols="50" rows="5" id="a_answer"></textarea>
</form>

Code (markup):

I have this form and when I click the link the text [link=PUT LINK HERE][/link] is entered into the textbox. Does anybody have any ideas how I could edit my current code so that when the link is clicked the user gets a little popup asking "Please enter the URL of your link:" (like here on DP) and the url that the user types in replaces the words "PUT LINK HERE"?.

Thanks

 

You mean something like this?

<script type="text/javascript">
function populate( ) {
   var value = prompt("Please enter the URL of your link:", "")
   document.forms[0].a_answer.value = "[link=" + value + "][/link]";
}
</script>

<a href="#" onclick="populate( );">
Link Here
</a>

<form id="form1" name="form1" method="post">
<textarea name="a_answer" cols="50" rows="5" id="a_answer"></textarea>
</form>

Code (markup):

 

Cheers
That works perfectly, thanks