开发环境： ``` <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script> ``` 生产环境 ``` <script src="https://cdn.jsdelivr.net/npm/vue"></script> ``` http://cdn.bootcss.com/vue/2.2.1/vue.js http://unpkg.com/vue-router@3.4.3/dist/vue-router.js