什么叫插件中methods ？

你在引用的插件源碼修改的？

可以先試一下有沒有Vue這個全局變量，在試一下Vue.$router

.
├── router
│?? └── index.js
├── any-where
│?? └── any-where.js
└── main.js

./main.js
=============
import Vue from 'vue'
import router from './router'
import SomeComponent from './SomeComponent'

new Vue({
  el: '#some-id',
  router,
  render: h => h(SomeComponent),
})

./router/index.js
=============
import Vue from 'vue'
import Router from 'vue-router'

Vue.use(Router)

const router = new Router({ ....... })

export default router

./any-where/any-where.js
=============
import router from '../router'

router.push({ name: 'xxxxxx' })