How to build a custom Sidebar Component in React

<code class="js">import React from 'react'
import ReactDOM from 'react-dom'
import { IndexLink, Link } from 'react-router'
import './Sidebar.scss'
import classNames from 'classnames'



class Sidebar extends React.Component {

    constructor(props) {
        super(props);
        this.state = {
            showMenu: false
        }
        this.toggleMenu = this.toggleMenu.bind(this)
    }
    componentDidMount() {
        document.addEventListener('click', this.handleClickOutside.bind(this), true);
    }

    componentWillUnmount() {
        document.removeEventListener('click', this.handleClickOutside.bind(this), true);
    }
    toggleMenu() {
        this.setState({ showMenu: !this.state.showMenu })
    }
    handleClickOutside(event) {
        const domNode = ReactDOM.findDOMNode(this);

        if ((!domNode || !domNode.contains(event.target))) {
            this.setState({
                showMenu: false
            });
        }
    }

    render() {

        const showMenu = this.state.showMenu;
        const sidebarClass = classNames({
            'sidebar': true,
            'sidebar-menu-expanded': showMenu,
            'sidebar-menu-collapsed': !showMenu
        });

        const elementsClass = classNames({
            'expanded-element': true,
            'is-hidden': !showMenu,
        });



    return (
      <nav className={sidebarClass}>
        <img
          className="menuIcon"
          src={menuIcon}
          onClick={this.toggleMenu}
        />
        <ul>
          <li>
            <Link className="expandable" to="/setting" title="Setting">
              <img
                src={'https://png.icons8.com/setting/ffffff'}
                alt=""
              />
              <span className={elementsClass}>Setting</span>
            </Link>
          </li>
        </ul>
      </nav>

        )
    }
}


export default Sidebar
<code class="sass">// Sidebar.scss
.menuIcon{
  margin-top: 70px;
  cursor: pointer;
}
nav.sidebar-menu-collapsed {
  width: 70px;
}

nav.sidebar-menu-expanded {
  width: 211px;
  z-index:1;
}

nav.sidebar {
  position: fixed;
  top: 0px;
  left: 0px;
  height: 100%;
  background: none repeat scroll 0 0 #000000;
  color: white;
  padding: 20px 10px;
}

nav.sidebar a#justify-icon {
  outline: 0;
  color: white;
  font-size: 24px;
  font-style: normal;
}

nav.sidebar ul {
  margin: 0;
  padding: 0;
  // margin-top: 60px;
}

nav.sidebar ul li {
  margin: 0;
  padding: 0;
  margin-top: 20px;
  list-style-type: none;
}

nav.sidebar ul li a.expandable {
  outline: 0;
  color: white;
  text-decoration: none;
  font-size: 20px;
}

nav.sidebar ul li a.expandable:hover {
  color: #bbbbbb;
}

nav.sidebar ul li a.expandable span.expanded-element {
  color: #FFF;
  margin-left: 12px;
  // display: none;
  font-size: 16px;
  position: relative;
  bottom: 2px;
}

nav.sidebar ul li.active {
  background: none repeat scroll 0 0 black;
  border-radius: 4px;
  text-align: center;
  margin-left: -4px;
  padding: 4px;
}

nav.sidebar ul li.active a.expandable {
  color: white !important;
}

nav.sidebar ul li.active a.expandable:hover {
  color: white !important;
}