Vue.js 2. Vue.use is not a function 错误

你好！

开始使用vue-router，但遇到错误：

Vue.use 不是函数

谷歌搜索，一无所获（谷歌上的白带）。

所有路径均已正确配置，模块已安装。

为什么会出现这个错误？

代码：

index.js（主文件，webpack 的入口点）

//require modules
const Vue = require('vue');
const VueRouter = require('vue-router');

// require components
const Index = require('../public/components/Index.vue');
const Items = require('../public/components/Items.vue');
const Users = require('../public/components/Users.vue');

const routes = [
    { path: '/', component: Index},
    { path: '/vue', component: Users},
    { path: '/news', component: Items}
];

//Setup routes
Vue.use(VueRouter);
const router = new VueRouter({
    routes,
    mode: 'history'
});

// Register components
new Vue({
    el: '#app',
    router,
    render: h => h(Index)
});

索引.vue

<template>
    <div id="app">
        <h1>Index</h1>
        <hr>
        <router-view></router-view>
    </div>
</template>

<script>
    export default {
        data: () => {return {}}
    }
</script>

错误：

webpack.config.js（可能不在配置中）

 const path = require('path');
const webpack = require('webpack');

module.exports = {
    entry: __dirname + "/public/index.js",
    output: {
        path: __dirname + "/public",
        filename: 'build.js',
        library: 'index'
    },
    module: {
        rules: [
            {
                test: /\.vue$/,
                loader: 'vue-loader',
                options: {
                    loaders: {}
                }
            }, {
                test: /\.js$/,
                loader: 'babel-loader',
                exclude: /node_modules/
            }, {
                test: /\.(png|jpg|gif|svg)$/,
                loader: 'file-loader',
                options: {
                    name: '[name].[ext]?[hash]'
                }
            }
        ]
    },
    resolve: {
        alias: {
            'vue$': 'vue/dist/vue.esm.js'
        }
    }
};