const headingGroup = this.$refs.preview.$el.querySelectorAll('h1,h2,h3,h4,h5,h6')
    for (let i = 0; i < headingGroup.length; ++i) {
          if (headingGroup[i].innerText === (anchor.title)) { 
            headingGroup[i].scrollIntoView({
              behavior: 'smooth',
              block: 'start'
            })
           }