Optimizing performance of the React list component

README.md

Optimizing performance of the React list component

Basically, everything need to be done in shouldComponentUpdate() method.

import React, {Component} from 'react';

class Item extends Component {
  shouldComponentUpdate(nextProps, nextState) {
    // always re-render component
    return true;
  }
  render() {
    return (
      <div/>
    );
  }
}

If we don’t mind compare all properties, we can use pre-defined implementation.

import React, {PureComponent} from 'react';

class Item extends PureComponent {
  render() {
    return (
      <div/>
    );
  }
}

Also we can create relevant enhancer much easier with recompose:

• shouldUpdate()
• pure()
• onlyUpdateForKeys()
• onlyUpdateForPropTypes()
• shallowEqual()

Demo

https://bl.ocks.org/mistakster/2d97a72814680d5069df214225c96a5d

It works only in Chrome and Firefox. See console for re-render updates.

app.js

(function () {

  /**
   * Helper function which creates initial list with mock data
   */
  function getInitialList() {
    return _.range(10)
      .map(n => ({
        id: n,
        title: `Item #${n}`,
        color: '#fff'
      }));
  }

  /**
   * Helper function which generates random value for the color component (red, green, blue)
   */
  function getRandomColorHexValue() {
    return Math.round(7 + 8 * Math.random()).toString(16);
  }

  /**
   * Dumb item component
   * It will print a message in console every time React invoke it
   */
  function ItemComponent({changeColor, item: {id, title, color}}) {
    console.log(`Render item: #${id}`);

    return React.createElement(
      'div',
      {
        style: {
          backgroundColor: color,
          padding: '10px',
          borderTop: '1px solid #ddd',
          borderBottom: '1px solid #ddd',
        }
      },
      React.createElement(
        'span',
        null,
        title
      ),
      React.createElement(
        'button',
        {
          onClick: changeColor,
          style: {
            marginLeft: '10px'
          }
        },
        'Change color'
      )
    )
  }

  /**
   * Item enhancer to apply optimizations and action hanlers
   */
  const Item = Recompose.compose(
    // This HOC is basically controlled version of `Recompose.pure` or React.PureComponent
    Recompose.shouldUpdate((props, nextProps) => {
      if (!props.optimization || props.optimization !== nextProps.optimization) {
        return true;
      }

      return !Recompose.shallowEqual(props, nextProps);
    }),
    Recompose.withHandlers({
      changeColor: props => () => {
        const {updateItem, item} = props;
        const r = getRandomColorHexValue();
        const g = getRandomColorHexValue();
        const b = getRandomColorHexValue();

        return updateItem({
          ...item,
          color: `#${r}${g}${b}`
        });
      }
    }),
    Recompose.mapProps(props => _.omit(props, ['updateItem']))
  )(ItemComponent);

  /**
   * Dumb list component
   */
  function ListComponent({list, optimization, updateItem, updateOptimization}) {
    return React.createElement(
      'div',
      null,
      React.createElement(
        'button',
        {
          onClick: () => {
            updateOptimization(!optimization);
          }
        },
        optimization ? 'Disable optimization' : 'Enable optimization'
      ),
      React.createElement(
        'div',
        {
          style: {
            marginTop: '10px'
          }
        },
        list.map(item => (
          React.createElement(Item, {key: item.id, updateItem, item, optimization})
        ))
      )
    );
  }

  /**
   * List enhancer which owns the state
   */
  const List = Recompose.compose(
    Recompose.withStateHandlers({
      list: getInitialList(),
      optimization: false
    }, {
      updateList: () => list => ({list}),
      updateOptimization: () => optimization => ({optimization})
    }),
    Recompose.withHandlers({
      updateItem: props => nextItem => {
        const {list, updateList} = props;

        updateList(list.map(item => {
          return item.id === nextItem.id ? nextItem : item
        }));
      }
    }),
    Recompose.mapProps(props => _.omit(props, ['updateList']))
  )(ListComponent);

  /**
   * Render the app
   */
  ReactDOM.render(
    React.createElement(List),
    document.getElementById('app')
  );

}());

index.html

<!DOCTYPE html>
<html>
<head>
  <title>Repaint</title>
</head>
<body>
<div id="app"></div>
<script crossorigin src="https://unpkg.com/react@16.2.0/umd/react.development.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@16.2.0/umd/react-dom.development.js"></script>
<script crossorigin src="https://unpkg.com/recompose@0.26.0/build/Recompose.js"></script>
<script crossorigin src="https://unpkg.com/lodash@4.17.4/lodash.js"></script>
<script src="app.js"></script>
</body>
</html>