button click event-- add script

Hello,
  I have a javascript function that I would like loaded to the head section when a button click happens. Is this possible? and how can I do it


here is script

<script type='text/javascript' src='https://www.dropbox.com/static/api/2/dropins.js' ></script>

Here is what I tying to accomplish. I want to add dropbox.js to my page and a dropbox picker. However, this service is block in  some network.So, my page load for a while if Drop Box is not allow. I would like to only incur this penalty when the button is press.

Thanks