Error in v-on handler: “TypeError: Cannot read properties of undefined (reading ‘concat’)” 错误原因: let arr = a.concat(b); 这句代码中,a不能为undefined,传数据出错了。 Error in v-on handler: “TypeError: Cannot read properties of undefined (reading ‘concat‘)“报错Error in v-on handler: “TypeError: Cannot read properties of undefined (reading ‘concat’)”