unpkg/client/Layout.js

import React from 'react'
import ReactDOM from 'react-dom'
import PropTypes from 'prop-types'
import { Motion, spring } from 'react-motion'
import { withRouter, Link } from 'react-router-dom'
import WindowSize from './WindowSize'

class Layout extends React.Component {
  static propTypes = {
    location: PropTypes.object,
    children: PropTypes.node
  }

  state = {
    underlineLeft: 0,
    underlineWidth: 0,
    useSpring: false
  }

  adjustUnderline = (useSpring = false) => {
    let itemIndex
    switch (this.props.location.pathname) {
      case '/about':
        itemIndex = 2
        break
      case '/stats':
        itemIndex = 1
        break
      case '/':
      default:
        itemIndex = 0
    }

    const itemNodes = ReactDOM.findDOMNode(this).querySelectorAll('.underlist > li')
    const currentNode = itemNodes[itemIndex]

    this.setState({
      underlineLeft: currentNode.offsetLeft,
      underlineWidth: currentNode.offsetWidth,
      useSpring
    })
  }

  componentDidMount() {
    this.adjustUnderline()
  }

  componentDidUpdate(prevProps) {
    if (prevProps.location.pathname !== this.props.location.pathname)
      this.adjustUnderline(true)
  }

  render() {
    const { underlineLeft, underlineWidth, useSpring } = this.state

    const style = {
      left: useSpring ? spring(underlineLeft, { stiffness: 220 }) : underlineLeft,
      width: useSpring ? spring(underlineWidth) : underlineWidth
    }

    return (
      <div>
        <WindowSize onChange={this.adjustUnderline}/>
        <div className="wrapper">
          <header>
            <h1>unpkg</h1>
            <nav>
              <ol className="underlist">
                <li><Link to="/">Home</Link></li>
                <li><Link to="/stats">Stats</Link></li>
                <li><Link to="/about">About</Link></li>
              </ol>
              <Motion defaultStyle={{ left: underlineLeft, width: underlineWidth }} style={style}>
                {s => (
                  <div
                    className="underlist-underline"
                    style={{
                      WebkitTransform: `translate3d(${s.left}px,0,0)`,
                      transform: `translate3d(${s.left}px,0,0)`,
                      width: s.width
                    }}
                  />
                )}
              </Motion>
            </nav>
          </header>
        </div>
        {this.props.children}
        <div className="wrapper">
          <footer>
            <p>&copy; 2016-{(new Date).getFullYear()} Michael Jackson</p>
          </footer>
        </div>
      </div>
    )
  }
}

export default withRouter(Layout)