How can I get the current velocity of a spring animation?

[trafnar]

I'm animating a custom value (not an element) with a spring, and I'd like to transfer the velocity to a new animation when it gets interrupted. Is there a way to obtain the current velocity of a running spring animation?

I know spring animations on dom elements get their velocity transferred automatically, how can I do it for this type of animation which uses a callback function?

I saw some discussion here #1 (reply in thread) that said:

Popmotion’s spring uses a velocity equation to figure out whether to stop on a given frame. I’ve modified that to expose this value - then if an animation is interrupted you can take the spring generator and scrub it to currentTime to get the velocity.

But I'm not sure if thats the right way, and I'm not sure how to "scrub the spring generator"

Any help would be appreciated, thanks!