怎么突然出现Vue is not defined的错误啦？

10:31:15.671 项目 'qni.mymall.mobile' 开始编译...
10:31:16.218 请注意运行模式下，因日志输出、sourcemap以及未压缩源码等原因，性能和包体积，均不及发行模式。
10:31:16.288 正在编译中...
10:31:16.757 INFO Starting development server...
10:31:22.911 App running at:
10:31:22.914 - Local: http://localhost:8081/
10:31:22.915 - Network: http://192.168.150.86:8081/
10:31:22.918 项目 'qni.mymall.mobile' 编译成功。前端运行日志，请另行在浏览器的控制台查看。
10:31:22.919 H5版常见问题参考: https://ask.dcloud.net.cn/article/35232
10:31:25.196 [HMR] Waiting for update signal from WDS...
10:31:25.208 [system]ReferenceError: Vue is not defined
at Function.success (webpack-internal:///./node_modules/babel-loader/lib/index.js!./node_modules/@dcloudio/vue-cli-plugin-uni/packages/webpack-preprocess-loader/index.js?!./node_modules/@dcloudio/vue-cli-plugin-uni/packages/webpack-preprocess-loader/index.js?!./node_modules/@dcloudio/vue-cli-plugin-uni/packages/webpack-uni-app-loader/using-components.js!./node_modules/@dcloudio/vue-cli-plugin-uni/packages/vue-loader/lib/index.js?!./node_modules/@dcloudio/vue-cli-plugin-uni/packages/webpack-scoped-loader/index.js!./node_modules/@dcloudio/vue-cli-plugin-uni/packages/wrap-loader/index.js?!../../../../../../Users/qianwei/Documents/Project/SpringBoot/qni.mymall/qni.mymall.mobile/App.vue?vue&type=script&lang=js&:7:9)
at http://localhost:8081/static/js/chunk-vendors.js:98:87021
at Object.j [as callback] (http://localhost:8081/static/js/chunk-vendors.js:98:89868)
at b (http://localhost:8081/static/js/chunk-vendors.js:98:90705)
at http://localhost:8081/static/js/chunk-vendors.js:98:91605
at O (http://localhost:8081/static/js/chunk-vendors.js:98:343220)
at Object.getSystemInfo (http://localhost:8081/static/js/chunk-vendors.js:98:535711)
at Vue.onLaunch (webpack-internal:///./node_modules/babel-loader/lib/index.js!./node_modules/@dcloudio/vue-cli-plugin-uni/packages/webpack-preprocess-loader/index.js?!./node_modules/@dcloudio/vue-cli-plugin-uni/packages/webpack-preprocess-loader/index.js?!./node_modules/@dcloudio/vue-cli-plugin-uni/packages/webpack-uni-app-loader/using-components.js!./node_modules/@dcloudio/vue-cli-plugin-uni/packages/vue-loader/lib/index.js?!./node_modules/@dcloudio/vue-cli-plugin-uni/packages/webpack-scoped-loader/index.js!./node_modules/@dcloudio/vue-cli-plugin-uni/packages/wrap-loader/index.js?!../../../../../../Users/qianwei/Documents/Project/SpringBoot/qni.mymall/qni.mymall.mobile/App.vue?vue&type=script&lang=js&:4:9)
at invokeWithErrorHandling (http://localhost:8081/static/js/chunk-vendors.js:5212:26)
at Vue.push../node_modules/@dcloudio/vue-cli-plugin-uni/packages/h5-vue/dist/vue.runtime.esm.js.Vue.__call_hook (http://localhost:8081/static/js/chunk-vendors.js:11954:17)
10:31:25.235 App Show at App.vue:29
10:31:25.252 Download the Vue Devtools extension for a better development experience:
https://github.com/vuejs/vue-devtools