mutationObservers() {
    // create an observer instance
    this.observer = new MutationObserver(mutations => {
      this.resizeCheck();
    }); // configuration of the observer:

    let config = {
      attributes: true,
      childList: true,
      characterData: true,
      subtree: true
    }; // pass in the target node, as well as the observer options

    this.observer.observe(this.document, config);
  }
Use MutationObserver to listen for changes in the DOM and check for resize
@private