Closest thing that I can think of is Vexflow which is a Javascript/HTML5 layout engine. It won't render Lilypond notation files directly (since Lilypond files are basically Scheme macros, it's difficult to get anything but Scheme to parse more complex Lilypond). If you absolutely need Lilypond parsed, you could hack Abjad, a Python package that can parse Lilypond, and maybe link it up with the Vexflow outputting mechanisms of my Python package music21. But you'd probably be better off making a pure Javascript converter to the Vexflow intermediate representation. It's hard stuff, but know that others are working on such things, so you're not alone.
