当使用enhanceApp.js并添加基本的代码后，无法渲染html文件

[cmlanche]

System:
OS: macOS Mojave 10.14.6
CPU: (4) x64 Intel(R) Core(TM) i5-7360U CPU @ 2.30GHz
Binaries:
Node: 10.13.0 - /usr/local/bin/node
Yarn: 1.17.3 - /usr/local/bin/yarn
npm: 6.4.1 - /usr/local/bin/npm
Browsers:
Chrome: 86.0.4240.111
Edge: Not Found
Firefox: Not Found
Safari: 13.0.4
npmPackages:
@vuepress/core: 1.7.1
@vuepress/theme-default: 1.7.1
vuepress: ^1.7.1 => 1.7.1
npmGlobalPackages:
vuepress: Not Found

enhanceApp.js的内容如下：

export default ({
  Vue, // VuePress 正在使用的 Vue 构造函数
  options, // 附加到根实例的一些选项
  router, // 当前应用的路由实例
  siteData, // 站点元数据
  isServer // 当前应用配置是处于 服务端渲染 或 客户端
}) => {
  router.beforeEach((to, from, next) => {
  })
}

当删除enhanceApp.js文件或者里面不写任何代码，能够正常生成html

• I confirm that this is an issue rather than a question.

Bug report

Steps to reproduce

What is expected?

能够正常将markdown文件渲染成html

What is actually happening?

assets的资源文件都生成了，比如css、img、js，一个HTML都没有生成，生成的日志中，没有出现success rendering html

Other relevant information

• Output of npx vuepress info in my VuePress project:

rowboat-docs@1.0.0 docs:build /Users/chengming/Documents/好未来/轻舟/docs
vuepress build .

wait Extracting site metadata...
tip Apply theme @vuepress/theme-default ...
tip Apply plugin container (i.e. "vuepress-plugin-container") ...
tip Apply plugin @vuepress/register-components (i.e. "@vuepress/plugin-register-components") ...
tip Apply plugin @vuepress/active-header-links (i.e. "@vuepress/plugin-active-header-links") ...
tip Apply plugin @vuepress/search (i.e. "@vuepress/plugin-search") ...
tip Apply plugin @vuepress/nprogress (i.e. "@vuepress/plugin-nprogress") ...

✔ Client
Compiled successfully in 18.36s

✔ Server
Compiled successfully in 14.53s

wait Rendering static HTML...

[cmlanche]

问题已解决，原因是如下代码不能ssr

router.beforeEach((to, from, next) => {
  })

需要做个判断：

if (isServer) {
router.beforeEach((to, from, next) => {
  })
}

[cnlydia]

I think use below is correct
router.beforeEach((to, from, next) => {
//xxx
next()
})