echarts如何让图表适应父级的尺寸

当父级没有明确尺寸时例如如下情况

<div class="chart-box">
  <div id="myChart" :style="{width: '100%', height: '100%'}"></div>
</div>

methods: {
    drawLine(){
        // 基于准备好的dom，初始化echarts实例
        let myChart = this.$echarts.init(document.getElementById('myChart'))
        // 绘制图表
        myChart.setOption({
            title: { text: '在Vue中使用echarts' },
            tooltip: {},
            xAxis: {
                data: ["衬衫","羊毛衫","雪纺衫","裤子","高跟鞋","袜子"]
            },
            yAxis: {},
            series: [{
                name: '销量',
                type: 'bar',
                data: [5, 20, 36, 10, 10, 20]
            }]
        });
    }
  }

.chart-box {
    flex: 1;
}

需要在dom加载完毕后进行echarts初始化
因此需要用到$nextTick()�函数
如果dom没加载完毕就初始化echarts无法获取父级的尺寸

 mounted() {
    this.$nextTick(() => {
      this.drawLine();
    });
 },