npm 不会启动反应应用程序，需要依赖项：“webpack-dev-server”：“3.1.14”

Question

I am trying to create a new react-app and start it, I have created react apps before with no errors but this time when i npm start i get this error

 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\ashraf\node_modules\webpack-dev-server (version: 3.1.9)

 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-dev-server" 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\ashraf\node_modules\webpack-dev-server is outside 
 your project directory.
 For example, you might have accidentally installed something in your home 
 folder.

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

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! learnreact@0.1.0 start: `react-scripts start`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the learnreact@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!     C:\Users\ashraf\AppData\Roaming\npm-cache\_logs\2019-02- 
04T20_36_39_924Z-debug.log
PS C:\Users\ashraf\Desktop\Files\LearnReact\learnreact>

i have tried all the steps in detail in the error log but its still not working, any thoughts on what is causing this error? Thanks in advance

Answer 1

It seems like you want to depend on webpack-dev-server inside your local project. Perhaps you need to run npm install in your project, instead of your ~ home directory?

from your output, notice these lines.

However, a different version of webpack-dev-server was detected higher up 
 in the tree:

 C:\Users\ashraf\node_modules\webpack-dev-server (version: 3.1.9)
...

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

so I would

cd ./my-project
npm i

Answer 2

Did you install webpack-dev-server on its own? It seems it has been installed either by you or by another project install. Webpack is for your local development environment so the other install is close enough to your project to interfere with the copy that react is trying to install in your project folder. Steps 1-4 in your error message should resolve your issue. If you have done that and its still not working, did you get different error messages with your next attempt to install your react package?

Answer 3

I have faced the same issue and this method worked for me.

Do follow the steps:

1. Start terminal from the desktop and write this command:

    npm uninstall webpack-dev-server

   This will uninstall webpack-dev-server package globally from you node modules.

2. Go back to you the terminal of your project and install webpack-dev-server package:

    npm install webpack-dev-server@version

   _{Note: The version part (above) should equal the versions asked for in the error message.}

    npm install webpack-dev-server

3. Now start npm:

    npm start

This error mostly occurs when you have created your project using the npx create-react-app command instead of the npm create-react-app command.