VueRouter is not defined

I have a laravel project and want use Vue.js for frontend. But i have never used something more complicated than jquery. I can't run vue-router.

In my app.js

require('./bootstrap');
require('./vue-router');
require('./routes');

window.Vue = require('vue');
     const app = new Vue({
     el: '#app',
});

Then i copy code vue-router from http://ift.tt/2Bxg3wu

In my routes.js

const router = new VueRouter();

var App = Vue.extend({});

router.start(App, '#app');

And when i try open page in console i see next : "VueRouter is not defined"

via Chebli Mohamed