constructor(props) {
    super(props);
    this.state = {
      style: {},
      visible: false,
      isOpen: false,
    };
    this.node = null;
    this.blockKey = '';
    this.blockType = '';
    this.blockLength = -1;

    this.findNode = this.findNode.bind(this);
    this.hideBlock = this.hideBlock.bind(this);
    this.openToolbar = this.openToolbar.bind(this);
  }
Implementation of the medium-link side `+` button to insert various rich blocks
like Images/Embeds/Videos.