react this.state 解构语法

把this.state的属性解构为独立的变量

写法1：

const data = this.state.data;
const yearStart = this.state.yearStart;
const yearEnd = this.state.yearEnd;
const svgRef = this.state.svgRef;

写法2:

简便写法

const { data, yearStart, yearEnd, svgRef } = this.state;