Gives you on screen output of JavaScript's console.log() on Android, iPhone, iPad and iPod.
Include console.js in your HTML file. Actually you could simply add this inside your head tag:
<script src="http://code.jquery.com/jquery-1.7.2.min.js" type="text/javascript"></script>
<script src="https://raw.github.com/gorbiz/mobile-console.log/master/console.js" type="text/javascript"></script>
Of course omit the first line if you already have jQuery included.