My entry for the 2012 JS1k competition. An interactive heart-shaped spirograph.
The lattice pattern is based on a hypotrochoid, but instead of rolling the inner cog around a circle it's rolled around a heart shape, described using the heart-curve equation.
813 bytes compressed, using the Google Closure compiler.
You can find the entry on the JS1k website here: http://js1k.com/2012-love/details/1232