title: what onEndReachedThreshold really means in react-native
body: <p><a href="https://facebook.github.io/react-native/docs/listview.html" rel="noreferrer">from documentation</a>:</p>
  
  <blockquote>
    <p>onEndReachedThreshold number </p>
  </blockquote>
  
  <p>Threshold in pixels (virtual, not physical) for calling onEndReached.
   so I just wanted to know what it means, is it threshold from the top, or is it threshold from the bottom.</p>
  
  <p>From the top? - if I set a value of onEndReachedThreshold ={10}, is my onEndReached called as soon as I scrolled to 10 pixel, or something else.</p>
  
  <p>From the bottom? - if I set value of  onEndReachedThreshold ={listview height -10}, will my onEndReached called as soon as I scrolled to 10 pixel, or something else.</p>