Vue-router error: TypeError: Cannot read property ‘matched’ of undefined

The name when you add it to Vue must be router.

import router from './routes.js'

const app = new Vue({
  el: '#app',
  router,
  render: h => h(App)
})

If, for whatever reason, you want to call the variable routes you could assign it this way.

import routes from './routes.js'

const app = new Vue({
  el: '#app',
  router: routes,
  render: h => h(App)
})