The two of you could probably bootstrap your expertise into a non-VC, multi-$M ARR Javascript performance consultancy, taking peoples code and finding 5-10X speed ups through better JavaScript.

You could have a great lifestyle and a great business after a few years of work and growing a team of skilled JS performance experts.

Eventually you would probably stumble your way into a solid product once you had solved enough customer problems to see the commonalities (or through your internal tooling etc).