依赖问题（ASP.NET Core + React.js）

Question

after creating a new ASP .NET Core (3.1) App with React.js project I'm trying to run it, but I'm getting a following error:

An unhandled exception occurred while processing the request.
AggregateException: One or more errors occurred. (One or more errors occurred. (The NPM script 'start' exited without indicating that the create-react-app server was listening for requests. The error output was:

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": "4.42.0"

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\xxxx\node_modules\webpack (version: 5.25.1)

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\xxx\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!

npm ERR! code ELIFECYCLE

npm ERR! errno 1

))
System.Threading.Tasks.Task.ThrowIfExceptional(bool includeTaskCanceledExceptions)

InvalidOperationException: The NPM script 'start' exited without indicating that the create-react-app server was listening for requests. The error output was:

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": "4.42.0"

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\xxx\node_modules\webpack (version: 5.25.1)

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\xxx\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!

I've tried following instructions included in this error, but then I'm running into a blank page with a 400 error. Does anyone knows how to fix it? I've tried everything I have found on the internet (also installing older version of webpack manually), but so far nothing seems to work.

Answer 1

To fix the problem you need the node package manager (npm) in addition to the dotnet 3.1 SDK.

You can download and install it here: https://nodejs.org/de/ (Whereby I would recommend chocolatey for Windows)

After the installation you can check your npm version with npm --version . If there is no answer and you are on Windows, you have to restart your computer once.

If npm is successfully installed, you have to navigate with the terminal (or powershell) to your project folder and run the command npm install to reinstall all dependencies.

If you still have problems installing all modules, you can check the package.json file to see which packages you have installed with which version and then simply update or delete packages there. After you have finished editing your package.json you have to run npm install again.

This is a general help on how you can get closer to your issue

Answer 2

I ran into this problem a while ago. Go to C:\Users\User there is a folder named node_modules delete it. don't run npm install... just go on VS (close and restart if its open) and create a new React.Net core project. VS terminal will download and install all the packages. This solved my problem.