// In general, you need polyfill,
// The recommended module is 'https://github.com/juggle/resize-observer'.

// import ResizeObserver from '@juggle/resize-observer'

new Vue({
  el: '#app',
  data () {
    return {
      width: 0,
      height: 0
    }
  },
  mounted () {
    this.observeSize()
  },
  methods: {
    observeSize () {
      const ro = new ResizeObserver(entries => {
        entries.forEach(entry => {
          const { width, height } = entry.contentRect
          this.width = width
          this.height = height
        })
      })
      
      ro.observe(this.$refs.targetElement)
    }
  }
})