如何在Vue2项目中引入echarts?

https://segmentfault.com/a/11... @Jinkey
学习这个项目最后引入了Element-ui 图片描述

我想在这个demo中插入echarts
main.js

HTML

<div id="main"></div>

export default {
    data() {
        return {
            a: 1,
            msg: 'Hello Vue!'
        }
    },
    methods: {
        add() {
            this.a++;
            console.log(this.a)
        }
    }
   // components :{ firstComponent,secondComponent }
}
var myChart = echarts.init(document.getElementById('main'));
console.log(myChart);
console.log(123)
// 绘制图表
myChart.setOption({
    title: { text: 'ECharts 入门示例' },
    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]
    }]
});

这样写为什么会报错