记一次vuepress报错：UnhandledPromiseRejectionWarning: TypeError: res.getHeader is not a function

在使用vuepress时，按照官网的操作：

在执行完vuepress之后，控制台出现：

VuePress dev server listening at http://localhost:8080/

当将  http://localhost:8080/   放入浏览器并确定时，会出现以下报错：

(node:8960) UnhandledPromiseRejectionWarning: TypeError: res.getHeader is not a function
    at processRequest (D:\刘威\AmyProject\0326\vuepress-homepage\node_modules\webpack-dev-middleware\lib\middleware.js:82:18)
    at ready (D:\刘威\AmyProject\0326\vuepress-homepage\node_modules\webpack-dev-middleware\lib\util.js:51:12)
    at handleRequest (D:\刘威\AmyProject\0326\vuepress-homepage\node_modules\webpack-dev-middleware\lib\util.js:167:5)
    at Promise (D:\刘威\AmyProject\0326\vuepress-homepage\node_modules\webpack-dev-middleware\lib\middleware.js:44:7)
    at new Promise (<anonymous>)
    at middleware (D:\刘威\AmyProject\0326\vuepress-homepage\node_modules\webpack-dev-middleware\lib\middleware.js:43:12)
    at Promise.all.Promise (D:\刘威\AmyProject\0326\vuepress-homepage\node_modules\koa-webpack\index.js:43:7)
    at new Promise (<anonymous>)
    at D:\刘威\AmyProject\0326\vuepress-homepage\node_modules\koa-webpack\index.js:42:5
    at dispatch (D:\刘威\AmyProject\0326\vuepress-homepage\node_modules\koa\node_modules\koa-compose\index.js:42:32)
    at D:\刘威\AmyProject\0326\vuepress-homepage\node_modules\@shellscape\koa-static\legacy\index.js:58:19
    at Generator.throw (<anonymous>)
    at step (D:\刘威\AmyProject\0326\vuepress-homepage\node_modules\@shellscape\koa-static\legacy\index.js:6:221)
    at _throw (D:\刘威\AmyProject\0326\vuepress-homepage\node_modules\@shellscape\koa-static\legacy\index.js:6:455)
(node:8960) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:8960) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future,
promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

在这个问题中，通过查找vuepress的issuse我知道是： webpack-dev-middleware 这个中间件的原因。

webpack-dev-middleware的作用就是：生成一个与webpack的compiler绑定的中间件，然后在express启动的服务app中调用这个中间件。

个人推测（通过issuse里讨论）：因为webpack-dev-middleware的版本过高，造成了不兼容，所以每次启动都会报这个错

解决方法便是手动设置webpack-dev-middleware的版本：

npm install webpack-dev-middleware@3.6.0

设置成3.6.0版本，然后再一次加载全部依赖：

npm install

最后再次启动项目即可