滑动列表数据按照A-Z首字母排列，右边A-Z能动态定位到相应字母位置

核心实现，循环右边字母列表，然后找出左边数据列表，对应id为相应字母的元素，计算元素到顶部和底部的距离，就是范围，然后滑动监听，通过滑动的距离在哪个范围确定右边要定位到哪个字母，实现最终效果：

this.$nextTick(() => {
        this.itemsParent = []
        for (let i = 0; i < this.listforgirht.length; i++) {
          const height = document.getElementById(this.listforgirht[i]).offsetHeight
          const top = document.getElementById(this.listforgirht[i]).offsetTop
          var items = { tag: '', topInstance: '', bottomInstance: '', position: '' }
          if (i === 1) {
            this.$set(items, 'tag', this.listforgirht[i])
            this.$set(items, 'topInstance', 0)
            this.$set(items, 'bottomInstance', height)
            this.$set(items, 'position', i)
          }
          this.$set(items, 'tag', this.listforgirht[i])
          this.$set(items, 'topInstance', top)
          this.$set(items, 'bottomInstance', top + height)
          this.$set(items, 'position', i)
          this.itemsParent.push(items)
        }
        console.log(this.itemsParent)
      })
    },
    scrollListen (event) {
      const top = event.target.scrollTop
      for (const item6 of this.itemsParent) {
        if (top >= item6.topInstance && top <= item6.bottomInstance) {
          const pos = item6.position
          this.indexm = pos
          console.log(pos)

          return
        }
      }
      console.log(event.target.scrollTop)

      console.log('123456')
    }