I'd recommend either killing that altogether as it definitely gives the perception of bad performance.
Or... at least take into account the delta of the progress change when doing animation. For instance, if going from 5 to 10%... a slower animation is fine. If going from 0 to 100%, the animation should be much quicker.
A lot of the work seems to be the React diffing? The only thing that changes between frames when dragging the slider is the style attribute.
Furthermore, the author seems to have included the development version of React. And the author used development settings for the webpack compilation. The compiled JS is full of eval() calls.
The think that myth is coming from the fact that JVM is heavy (150MB?), so it takes time to start, and hot-spot needs some iterations on a source code before it can fully apply JIT, but other that that, Java is really good.
I'd recommend either killing that altogether as it definitely gives the perception of bad performance.
Or... at least take into account the delta of the progress change when doing animation. For instance, if going from 5 to 10%... a slower animation is fine. If going from 0 to 100%, the animation should be much quicker.