Attempting to add types to pluck() after chat with TypeScript PM @DanielRosenwasser.
Here's the same attempt in a TS playground.
It doesn't seem to be working. For instance, this code:
const stream$ = undefined as MotionObservable<Point2D>; stream$.pluck('x')._map(value => value.toFixed());
results in "toFixed does not exist on type Pick<Point2D, 'x'>", even though x is a number on Point2D.