在写vue项目时，浏览器的console出现如下警告信息：
[Vue warn]: Property or method "index" is not defined on the instance but referenced during render. Make sure that this property is reactive, either in the data option, or for class-based components, by initializing the property. See: https://vuejs.org/v2/guide/reactivity.html#Declaring-Reactive-Properties. found in ---> <Navheader> at E:\GitRepository\companyProject\src\components\crimalcheck\crimalcheck.vue <App> at E:\GitRepository\companyProject\src\App.vue <Root>
原因很简单：不熟悉或者粗心的情况下很容易把v-for循环写成如下形式
<td v-for="item in xxx" :key="index" >
正确的写法应为<td v-for="(item,index) in xxx" :key="index" >
ps:把:key="index"删掉也可以解决此警告，但是这样就违反了Vue文档当中的推荐写法，v-for当中最好还是把:key写上