old_contents: import React from 'react';
  
  class Messenger extends React.Component {
    render() {
      return (
        <article className="c-messenger">
          <button className="c-messenger__attachment" onClick={this._toggleAttachment.bind(this)}>
            <i className="icon-add-circle-outline"></i>
          </button>
  
          <textarea placeholder="Share knowledge"></textarea>
  
          <button className="c-messenger__submit">
            <i className="icon-send"></i>
          </button>
        </article>
      );
    }
  
    _toggleAttachment() {
      console.log('set class to: state-active');
    }
  }
  
  export default Messenger;
  
new_contents: import React from 'react';
  
  class Messenger extends React.Component {
    constructor(props, context) {
      super(props, context);
  
      this.state = {
        showAttachment: false
      };
    }
  
    render() {
      let messengerAttachmentClass = `c-messenger__attachment ${this.state.showAttachment ? 'state-active' : ''}`;
  
      return (
        <article className="c-messenger">
          <button className={messengerAttachmentClass} onClick={this._toggleAttachment.bind(this)}>
            <i className="icon-add-circle-outline"></i>
          </button>
  
          <textarea placeholder="Share knowledge"></textarea>
  
          <button className="c-messenger__submit">
            <i className="icon-send"></i>
          </button>
        </article>
      );
    }
  
    _toggleAttachment() {
      this.setState({
        showAttachment: !this.state.showAttachment
      });
    }
  }
  
  export default Messenger;
  
subject: add attachment state to messenger component