yarn start, npm start 报错

报错信息如下：

C:\Users\Administrator\Desktop\web\lent>yarn start
yarn run v1.19.0
$ 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": "4.41.0"

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\Administrator\node_modules\webpack (version: 4.27.1)

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

If you would prefer to ignore this check, add SKIP_PREFLIGHT_CHECK=true to an .env file in your project.
That will permanently disable this message but you might encounter other issues.

To fix the dependency tree, try following the steps below in the exact order:

  1. Delete package-lock.json (not package.json!) and/or yarn.lock in your project folder.
  2. Delete node_modules in your project folder.
  3. Remove "webpack" from dependencies and/or devDependencies in the package.json file in your project folder.
  4. Run npm install or yarn, depending on the package manager you use.

In most cases, this should be enough to fix the problem.
If this has not helped, there are a few other things you can try:

  5. If you used npm, install yarn (http://yarnpkg.com/) and repeat the above steps with it instead.
     This may help because npm has known issues with package hoisting which may get resolved in future versions.

  6. Check if C:\Users\Administrator\node_modules\webpack is outside your project directory.
     For example, you might have accidentally installed something in your home folder.

  7. Try running npm ls webpack in your project folder.
     This will tell you which other package (apart from the expected react-scripts) installed webpack.

If nothing else helps, add SKIP_PREFLIGHT_CHECK=true to an .env file in your project.
That would permanently disable this preflight check in case you want to proceed anyway.

P.S. We know this message is long but please read the steps above :-) We hope you find them helpful!

error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

看报错解决方法提示：

If you would prefer to ignore this check, add SKIP_PREFLIGHT_CHECK=true to an .env file in your project.
That will permanently disable this message but you might encounter other issues.

如果您希望忽略此检查，请将SKIP_PREFLIGHT_CHECK=true添加到项目中的.env文件。这将永久禁用此消息，但您可能会遇到其他问题。

 

之前一直用的npm， 改用yarn 一个react项目后

npm install yarn -g

yarn create react-app xxxx

yarn start 就出现以上报错，

刚开始我是按照 错误提示的 7个步骤来走，把文件一个个都删了，然后在yarn start 然后没解决，所以还是在项目文件夹中新建  .env文件，在文件中添加

SKIP_PREFLIGHT_CHECK=true ，然后在yarn start 就ok了

 

解决方法：

　　在项目文件夹中新建  .env文件，在文件中添加 SKIP_PREFLIGHT_CHECK=true ，然后在yarn start 就ok了