Another way is to use meta tags. Whatever data is supposed to be passed to your JavaScript can be assigned like this:
<meta name="yourdata" content="whatever" />
<meta name="moredata" content="more of this" />
The data can then be pulled from the meta tags like this (best done in a DOMContentLoaded event handler):
var data1 = document.getElementsByName('yourdata')[0].content;
var data2 = document.getElementsByName('moredata')[0].content;
Absolutely no hassle with jQuery or the likes, no hacks and workarounds necessary, and works with any HTML version that supports meta tags...