Function To Retrieve The Value From Click Event?

I have create function to retrieve the value from click event. But the variable still undefined.

Code:
<span class="dialink" onclick="get_song('s1')">Send</span>
Code:
<script type="text/javascript" language="javascript">

[Code]....

Then I have create another section to show the value of that variable but it shows undefined.

Code:

<script type="text/javascript" language="javascript">document.writeln(song_title);</script>