创建反应应用程序后反应 npm start 不起作用

Question

我正在学习 React 而我的英语很差。 我已经有两个反应项目，但它们也不起作用:(我按照以下步骤操作，

npx create-react-app my-app cd my-app npm start

但它不起作用。 我再次尝试清理缓存和 npm install 但没有成功。 我该如何解决这个问题？

> my-app@0.1.0 start /Users/edu/Documents/htdocs/my-app
> 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:

  "babel-loader": "8.0.5"

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

  /Users/edu/node_modules/babel-loader (version: 8.1.0) 

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 "babel-loader" 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 /Users/edu/node_modules/babel-loader is outside your project directory.
     For example, you might have accidentally installed something in your home folder.

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

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!

npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! my-app@0.1.0 start: `react-scripts start`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the my-app@0.1.0 start script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/edu/.npm/_logs/2020-09-17T00_43_20_777Z-debug.log

Answer 1

查看输出中的建议编号 6。

检查 /Users/edu/node_modules/babel-loader 是否在您的项目目录之外。 例如，您可能不小心在主文件夹中安装了某些东西。

听起来好像在某个时候你不小心在你的主文件夹（ /Users/edu/ ）而不是你的项目文件夹中做了一个 npm install ，并且你的项目正在接受这个依赖。

修复方法是从/Users/edu/删除 node_modules、package.json 和 package-lock.json，这些不需要在那里。

对于其他 Google 员工：上述修复可能无法解决您的具体问题 - 仔细阅读错误消息，看看其他建议是否有帮助。 很多时候错误消息是非常无用的，但每隔一段时间，就会有人花时间写出一些有用的东西。 这是那些做得好的错误之一。

Answer 2

也许尝试：

npm cache clean

npm install

npm create-react-app my-app

cd my-app

npm run start