/**

 * Copyright (c) Meta Platforms, Inc. and its affiliates.

 *

 * This source code is licensed under the MIT license found in the

 * LICENSE file in the root directory of this source tree.

 *

 * @flow

 */

import * as React from 'react';

function generateArray(size: number) {

  return Array.from({length: size}, () => Math.floor(Math.random() * size));

}

const arr = generateArray(50000);

export default function LargeSubtree(): React.Node {

  const [showList, setShowList] = React.useState(false);

  const toggleList = () => {

    const startTime = performance.now();

    setShowList(!showList);

    // requestAnimationFrame should happen after render+commit is done

    window.requestAnimationFrame(() => {

      const afterRenderTime = performance.now();

      console.log(

        `Time spent on ${showList ? 'unmounting' : 'mounting'} the subtree: ${

          afterRenderTime - startTime

        }ms`,

      );

    });

  };

  return (

    <div>

      <h2>Mount/Unmount a large subtree</h2>

      <p>Click the button to toggle the state. Open console for results.</p>

      <button onClick={toggleList}>toggle</button>

      <ul>

        <li key="dummy">dummy item</li>

        {showList && arr.map((num, idx) => <li key={idx}>{num}</li>)}

      </ul>

    </div>

  );

}