redux-devtools/extension/examples/todomvc/components/Footer.js

import React, { Component } from 'react';
import PropTypes from 'prop-types';
import classnames from 'classnames';
import {
  SHOW_ALL,
  SHOW_COMPLETED,
  SHOW_ACTIVE,
} from '../constants/TodoFilters';

const FILTER_TITLES = {
  [SHOW_ALL]: 'All',
  [SHOW_ACTIVE]: 'Active',
  [SHOW_COMPLETED]: 'Completed',
};

class Footer extends Component {
  renderTodoCount() {
    const { activeCount } = this.props;
    const itemWord = activeCount === 1 ? 'item' : 'items';

    return (
      <span className="todo-count">
        <strong>{activeCount || 'No'}</strong> {itemWord} left
      </span>
    );
  }

  renderFilterLink(filter) {
    const title = FILTER_TITLES[filter];
    const { filter: selectedFilter, onShow } = this.props;

    return (
      <a
        className={classnames({ selected: filter === selectedFilter })}
        style={{ cursor: 'pointer' }}
        onClick={() => onShow(filter)}
      >
        {title}
      </a>
    );
  }

  renderClearButton() {
    const { completedCount, onClearCompleted } = this.props;
    if (completedCount > 0) {
      return (
        <button className="clear-completed" onClick={onClearCompleted}>
          Clear completed
        </button>
      );
    }
  }

  render() {
    return (
      <footer className="footer">
        {this.renderTodoCount()}
        <ul className="filters">
          {[SHOW_ALL, SHOW_ACTIVE, SHOW_COMPLETED].map((filter) => (
            <li key={filter}>{this.renderFilterLink(filter)}</li>
          ))}
        </ul>
        {this.renderClearButton()}
      </footer>
    );
  }
}

Footer.propTypes = {
  completedCount: PropTypes.number.isRequired,
  activeCount: PropTypes.number.isRequired,
  filter: PropTypes.string.isRequired,
  onClearCompleted: PropTypes.func.isRequired,
  onShow: PropTypes.func.isRequired,
};

export default Footer;