I've recently updated my Spine JavaScript runtime to support some of the new features in Spine; including IK constraints and free-form deformation.
https://github.com/flyover/spine.js
There is also an demo with both WebGL and Canvas renderers. The WebGL renderer does the bone blending and free-form deformation mixing on the GPU. The Canvas renderer supports regions, meshes and skinned mesh attachments, including FFD. I'm still looking for a solution for slot color in the Canvas renderer.
I've tested with most of the examples I could find online. I'm looking for more examples to test and feedback on what needs to be fixed. Thanks!