安装vant-ui常用方式，最方便的一种

//1.安装babel-plugin-import

npm install babel-plugin-import --save-dev

//2.在.babel中添加配置

 "plugins": [
    "transform-vue-jsx",
    "transform-runtime",
    ["import",{"libraryName":"vant","style":true}]
  ]

3.npm i vant -S 安装vant

//4.在vue组件中的使用

<template>
  <van-rate v-model="val"></van-rate>    
</template>
<script>
import { Rate } from 'vant'
export default {
  components: {  
    [Rate.name]: Rate
  },
  data() {
    return {
      val: 5
    }
  }
</script>