Change e.getSession().setMode(...)
to "ace/mode/<language>" where <language> is your preferred programming language to have proper syntax highlighting. Then copy and paste the code into your browser bar and edit away :D.
data:text/html,
<div class="e" style="position: absolute; top: 0; right: 0; bottom: 0; left: 0;" id="editor"></div>
<script src="http://d1n0x3qji82z53.cloudfront.net/src-min-noconflict/ace.js" type="text/javascript" charset="utf-8"></script>
<script>
var e = ace.edit("editor");
e.setTheme("ace/theme/monokai");
e.getSession().setMode("ace/mode/javascript");
</script>