text: import React,{Component} from 'react';
  import {Link} from 'react-router-dom';
  
  export default class Header extends Component{
    render () {
      return (
      <header>
        <nav className="navbar navbar-default">
          <div className="container">
            <div className="navbar-header">
              <button type="button" className="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1">
                <span className="sr-only">Toggle navigation</span>
                <span className="icon-bar"></span>
                <span className="icon-bar"></span>
                <span className="icon-bar"></span>
              </button>
              <Link className="navbar-brand" to={'/'}>Home</Link>
            </div>
  
            <div className="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
              <ul className="nav navbar-nav">
                <li className="active">
                  <Link to={`/books/all`}>Books <span className="sr-only">(current)</span></Link>
                </li>
                <li>
                  <Link to={`/authors/`}>Authors</Link>
                </li>
              </ul>
  
              <ul className="nav navbar-nav navbar-right">
                <li>
                  <Link to={'/'}>Right</Link>
                </li>
              </ul>
            </div>
          </div>
        </nav>
      </header>
      )
    }
  }