index.html页面引入

    <link rel="stylesheet" href="plug/element-ui/theme-chalk/index.css" rel="external nofollow" >
    <script src="js/vue.min.js"></script>
    <script src="js/vue-router.min.js"></script>
     <script src="js/axios.min.js"></script>
    <script src="plug/element-ui/element-ui.js"></script>

在vue.config.js页面设置

configureWebpack: {
        externals: {
            'vue': 'Vue',
            'vue-router':'VueRouter',
            'axios':'axios',
            'element-ui':'ElementUI'
          },
        plugins: [
            new webpack.ProvidePlugin({
                $: 'jquery',
                jQuery: 'jquery',
                'windows.jQuery': 'jquery',
            })
        ]
    },

报错:vue-router.min.js:6 ReferenceError: ElementUI is not defined

解决:

cdn 版本的 element-ui 设置的全局变量是 ELEMENT

configureWebpack: {
        externals: {
            'vue': 'Vue',
            'vue-router':'VueRouter',
            'axios':'axios',
            'element-ui':'ELEMENT'
          },
        plugins: [
            new webpack.ProvidePlugin({
                $: 'jquery',
                jQuery: 'jquery',
                'windows.jQuery': 'jquery',
            })
        ]
    },