vue报错 Property or method “index“ is not defined on the instance but referenced during render.

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.

数据没有初始化

在vue的data定义一个初始值

 data () {
   return {
     index: 0,
   }
 }

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