<div id="react-root">
</div>

html {
  background-color: gray;
}

.container {
  background-color: white;
  width: 600px;
  margin: 20px auto;
}

const renderCounts = new Array(10000).fill(0);

function rowRenderer ({ index, isScrolling, key, style }) {
  renderCounts[index]++;
  return (
    <div key={key} style={style}>
      Item {index}  (rendered {renderCounts[index]} times)
    </div>
  );
};

ReactDOM.render(
  <div className="container">
    <ReactVirtualized.List
      width={600}
      height={600}
      rowCount={10000}
      rowHeight={20}
      rowRenderer={rowRenderer}
    />
  </div>,
    
  document.getElementById('react-root')
);
console.dir(ReactVirtualized);