解決create-react-app 后 npm start 中出現 的webpack版本問題和webpack-dev-server的版本問題

利用VSCode搭建react的腳手架運行環境的時候。create-react-app之后npm start出現如下圖的問題：

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.

在參考 https://blog.csdn.net/muzi190/article/details/84108714 之后，又出現如下的問題。。。：

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.

解決辦法：找到版本出問題的目錄：如我的是

C:\Users\17720\node_modules\

然后在該路徑（這是全局路徑）下卸載不符合版本的webpack 與 webpack-dev-server

注意卸載webpack時還需要卸載webpack-cli ，4.0版本后的webpack都帶有webpack-cli:

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

然后再把提示報錯的版本安裝上，如:

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

這時候再次npm start 就沒出現問題啦