index.html

<!DOCTYPE html>
<html>

  <head>
    <meta charset="utf-8">
    <title>Reactjs in 40 </title>
    <style media="screen">
      .like-btn { font-size: 50px; }
    </style>
  </head>

  <body>
    <div class='wrapper'></div>
  </body>

  <script type="text/javascript">
    /* Component */
    class Component {
      constructor (props = {}) {
        this.props = props
      }

      setState (state) {
        const oldEl = this.el
        this.state = state
        this.el = this.renderDOM()
        if (this.onStateChange) this.onStateChange(oldEl, this.el)
      }

      renderDOM () {
        this.el = createDOMFromString(this.render())
        if (this.onClick) {
          this.el.addEventListener('click', this.onClick.bind(this), false)
        }
        return this.el
      }
    }

    const createDOMFromString = (domString) => {
      const div = document.createElement('div')
      div.innerHTML = domString
      return div
    }

    const mount = (component, wrapper) => {
      wrapper.appendChild(component.renderDOM())
      component.onStateChange = (oldEl, newEl) => {
        wrapper.insertBefore(newEl, oldEl)
        wrapper.removeChild(oldEl)
      }
    }

    /* ========================================= */
    class LikeButton extends Component {
      constructor (props) {
        super(props)
        this.state = { isLiked: false }
      }

      onClick () {
        this.setState({
          isLiked: !this.state.isLiked
        })
      }

      render () {
        return `
          <button class='like-btn' style="background-color: ${this.props.bgColor}">
            <span class='like-text'>
              ${this.state.isLiked ? '取消' : '点赞'}
            </span>
            <span>👍</span>
          </button>
        `
      }
    }

    class RedBlueButton extends Component {
      constructor (props) {
        super(props)
        this.state = {
          color: 'red'
        }
      }

      onClick () {
        this.setState({
          color: 'blue'
        })
      }

      render () {
        return `
          <div style='color: ${this.state.color};'>${this.state.color}</div>
        `
      }
    }

    const wrapper = document.querySelector('.wrapper')
    mount(new LikeButton({ bgColor: 'red' }), wrapper)
    mount(new LikeButton(), wrapper)
    mount(new RedBlueButton(), wrapper)
  </script>
</html>