React Native - how to scroll a ScrollView to a given location after navigation from another screen

I read that you can pass in parameters when using the StackNavigator like so: but I don't know how to read out that parameter in my Items screen.

That is achieved by accessing this.props.navigation.state.params inside your child component.

I think the best time to call scrollTo on your scrollview reference is when it first gets assigned. You're already giving it a reference and running a callback function - I would just tweak it so that it also calls scrollTo at the same time:

export default class Items extends React.Component {
  render(){
    let scrollItems = [] //Somecode that generates and array of items
    const {id} = this.props.navigation.state.params;

    return (
      <View>
        <View style={styles.scrollViewContainer}>
          <ScrollView 
          horizontal
          pagingEnabled
          ref={(ref) => {
            this.myScroll = ref
            this.myScroll.scrollTo() // !!
          }>
            {scrollItems}
          </ScrollView>
        </View>
      </View>
    )
  }  
}

And this is why I use FlatLists or SectionLists (which inherit from VirtualizedList) instead of ScrollViews. VirtualizedList has a scrollToIndex function which is much more intuitive. ScrollView's scrollTo expects x and y parameters meaning that you would have to calculate the exact spot to scroll to - multiplying width of each scroll item by the index of the item you're scrolling to. And if there is padding involved for each item it becomes more of a pain.