vue运行报错：SyntaxError: Cannot use import statement outside a module

PS C:\Users\wangting\Desktop\assets_web_admin\assets_web_admin> npm run dev
> vue-element-admin@4.2.1 dev C:\Users\wangting\Desktop\assets_web_admin\assets_web_admin
> vue-cli-service serve
 INFO  Starting development server...
 10% building 2/2 modules 0 active ERROR  SyntaxError: Cannot use import statement outside a module
C:\Users\wangting\Desktop\assets_web_admin\assets_web_admin\mock\index.js:1
import "core-js/modules/es6.regexp.constructor";
^^^^^^
SyntaxError: Cannot use import statement outside a module
    at wrapSafe (internal/modules/cjs/loader.js:1072:16)
    at Module._compile (internal/modules/cjs/loader.js:1122:27)
    at Module._compile (C:\Users\wangting\Desktop\assets_web_admin\assets_web_admin\node_modules\pirates\lib\index.js:99:24)
    at Module._extensions..js (internal/modules/cjs/loader.js:1178:10)
    at Object.newLoader [as .js] (C:\Users\wangting\Desktop\assets_web_admin\assets_web_admin\node_modules\pirates\lib\index.js:104:7)
    at Module.load (internal/modules/cjs/loader.js:1002:32)
    at Function.Module._load (internal/modules/cjs/loader.js:901:14)
    at Module.require (internal/modules/cjs/loader.js:1044:19)
    at require (internal/modules/cjs/helpers.js:77:18)
    at registerRoutes (C:\Users\wangting\Desktop\assets_web_admin\assets_web_admin\mock\mock-server.js:11:30)
    at Object.module.exports [as before] (C:\Users\wangting\Desktop\assets_web_admin\assets_web_admin\mock\mock-server.js:57:22)
    at Object.before (C:\Users\wangting\Desktop\assets_web_admin\assets_web_admin\node_modules\@vue\cli-service\lib\commands\serve.js:165:67)
    at Server.setupBeforeFeature (C:\Users\wangting\Desktop\assets_web_admin\assets_web_admin\node_modules\webpack-dev-server\lib\Server.js:455:18)
    at Object.before (C:\Users\wangting\Desktop\assets_web_admin\assets_web_admin\node_modules\webpack-dev-server\lib\Server.js:515:16)
    at C:\Users\wangting\Desktop\assets_web_admin\assets_web_admin\node_modules\webpack-dev-server\lib\Server.js:584:24
    at Array.forEach (<anonymous>)

VUE_CLI_BABEL_TRANSPILE_MODULES = true

# just a flag
ENV = 'development'
# base api
VUE_APP_BASE_API = '/dev-api'
# vue-cli uses the VUE_CLI_BABEL_TRANSPILE_MODULES environment variable,
# to control whether the babel-plugin-dynamic-import-node plugin is enabled.
# It only does one thing by converting all import() to require().
# This configuration can significantly increase the speed of hot updates,
# when you have a large number of pages.
# Detail:  https://github.com/vuejs/vue-cli/blob/dev/packages/@vue/babel-preset-app/index.js
VUE_CLI_BABEL_TRANSPILE_MODULES = true