Undocumented props. Why?

Anyway.

onMomentumScrollEnd will fire when the animation of the ScrollView stops.

For example, you can use the following snippet, to get the Y position of a <ScrollView ref="scrollView" />:

const RCTUIManager = require('NativeModules').UIManager
const sv = this.refs['scrollView'] as any
RCTUIManager.measure(sv.getInnerViewNode(), (...data) => {
  console.log(data[5])
})

And this is the order in which events of a ScrollView fire, in case you ever find yourself looking for answers that can’t be found in the official docs.

onTouchStart={() => console.log('onTouchStart')}
onTouchMove={() => console.log('onTouchMove')}
onTouchEnd={() => console.log('onTouchEnd')}
onScrollBeginDrag={() => console.log('onScrollBeginDrag')}
onScrollEndDrag={() => console.log('onScrollEndDrag')}
onMomentumScrollBegin={() => console.log('onMomentumScrollBegin')}
onMomentumScrollEnd={() => console.log('onMomentumScrollEnd')}

Reference:

http://stackoverflow.com/a/33924777/2621748