解决create-react-app 后 npm start 中出现 的webpack版本问题和webpack-dev-server的版本问题

利用VSCode搭建react的脚手架运行环境的时候。create-react-app之后npm start出现如下图的问题：

There might be a problem with the project dependency tree.
It is likely not a bug in Create React App, but something you need to fix locally.

The react-scripts package provided by Create React App requires a dependency:

  "webpack": "4.19.1"

Don't try to install it manually: your package manager does it automatically.
However, a different version of webpack was detected higher up in the tree:

  C:\Users\17720\node_modules\webpack (version: 4.25.1)

(version: 2.9.1) Manually installing incompatible versions is known to cause hard-to-debug issues.

在参考 https://blog.csdn.net/muzi190/article/details/84108714 之后，又出现如下的问题。。。：

PS C:\Users\17720\Desktop\Study\React\hello> npm start

> hello@0.1.0 start C:\Users\17720\Desktop\Study\React\hello
> react-scripts start

There might be a problem with the project dependency tree.
It is likely not a bug in Create React App, but something you need to fix locally.

The react-scripts package provided by Create React App requires a dependency:

  "webpack-dev-server": "3.1.14"

Don't try to install it manually: your package manager does it automatically.
However, a different version of webpack-dev-server was detected higher up in the tree:

  C:\Users\17720\node_modules\webpack-dev-server (version: 2.9.1)

Manually installing incompatible versions is known to cause hard-to-debug issues.

解决办法：找到版本出问题的目录：如我的是

C:\Users\17720\node_modules\

然后在该路径（这是全局路径）下卸载不符合版本的webpack 与 webpack-dev-server

注意卸载webpack时还需要卸载webpack-cli ，4.0版本后的webpack都带有webpack-cli:

npm un webpack
npm un webpack-cli
npm un webpack-dev-server

然后再把提示报错的版本安装上，如:

npm i webpack@4.19.1
npm i webpack-cli
npm i webpack-dev-server@3.1.14

这时候再次npm start 就没出现问题啦