Vue-懒加载(判断元素是否在可视区域内)

上公式：

元素距离顶部高度（elOffsetTop） >= dom滚动高度（docScrollTop）
并且元素距离顶部高度（elOffsetTop） < （dom滚动高度 + 视窗高度）

上代码：

一个多图表 懒加载 例子

<template>
  <div :id="boxId" style="height: 450px">
    <div v-loading="chartLoading">
      <defect-flight-pattern-chart
        :chart-data="chartData"
        :chart-id="chartId">
      </defect-flight-pattern-chart>
    </div>
  </div>
</template>

<script>
import DefectFlightPatternChart from '~/components/metrics/defect-flight-pattern-chart'
export default {
  components: {
    DefectFlightPatternChart
  },
  props: {
    projectUuid: { type: String, default: '' },
    chartIndex: { type: Number, default: 0 }
  },
  data () {
    return {
      chartData: {},
      chartLoading: false,
      isLoaded: false,
      boxId: 'dashboard-chart-box-',
      chartId: 'dashboard-chart-'
    }
  },
  mounted () {
    this.chartId = this.chartId + this.chartIndex + Math.floor(Math.random() * 1000)
    this.boxId = this.chartId + '-box'
    this.$nextTick(() => {
      this.scroll()
      window.addEventListener('scroll', this.scroll)
    })
  },
  destroyed () {
    window.removeEventListener('scroll', this.scroll, false)
  },
  methods: {
    async getChartData () {
      try {
        this.isLoaded = true
        this.chartLoading = true
        const { data } = await this.$axios.get(`/api/v1/projects/${this.projectUuid}/issues/trend`)
        this.chartData = data
        this.chartLoading = false
      } catch (e) {
        console.log(e)
      }
    },
    async scroll () {
      const elOffsetTop = document.getElementById(this.boxId).offsetTop
      const docScrollTop = document.documentElement.scrollTop - 230
      if (elOffsetTop >= docScrollTop && elOffsetTop < (docScrollTop + window.innerHeight) && !this.isLoaded) {
        await this.getChartData()
      }
    }
  }
}
</script>

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