At present lib/javascript.php calls 7 JS files out of which 6 are static.

<script type="text/javascript" src="<?php echo $CFG->httpswwwroot ?>/lib/javascript-static.js"></script>
<script type="text/javascript" src="<?php echo $CFG->httpswwwroot ?>/lib/overlib/overlib.js"></script>
<script type="text/javascript" src="<?php echo $CFG->httpswwwroot ?>/lib/overlib/overlib_cssstyle.js"></script>
<script type="text/javascript" src="<?php echo $CFG->httpswwwroot ?>/lib/cookies.js"></script>
<script type="text/javascript" src="<?php echo $CFG->httpswwwroot ?>/lib/ufo.js"></script>
<script type="text/javascript" src="<?php echo $CFG->httpswwwroot ?>/lib/dropdown.js"></script>

All these files can be combined to a single JS file to reduce number of HTTP connections. Recommended by yslow.