Vue project install is normal. When NPM run dev is started, the project cannot be started due to warnings.

Exception prompt:

(Emitted value instead of an instance of Error)
 <el-row v-for="item in order.products">: component lists rendered with v-for should have explicit keys. 
 See https://vuejs.org/guide/list.html#key for more info.

Anomaly analysis:

On the child elements of the transition-group tag, do not use the v-for index as the key, otherwise it is the same as not using the key

Solution:
V-for specifies subscript, :key="index"