The NPM script 'start' exited without indicating that the Angular CLI was listening for requests

Question

I'm attempting to start an .NET Core 2/Angular 6 SPA. I created an Angular 5 Application using "dotnet new angular" then proceeded to upgrade using this guide from angular.io. Once I finished the upgrade I tried to run the application using "dotnet run" and I get an ugly error page with the 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 Angular CLI was listening for requests. The error output was: Unknown option: '--extractCss'

InvalidOperationException: The NPM script 'start' exited without indicating that the Angular CLI was listening for requests. The error output was: Unknown option: '--extractCss'

Thinking perhaps I missed a step during the upgrade, I tried a second time and got the same error.

Here are the steps I took after creating the app:

npm install -g @angular/cli
npm install @angular/cli
ng update @angular/cli
ng update @angular/core
npm install --save @angular/material @angular/cdk @angular/animations hammerjs 
npm install -g rxjs-tslint
rxjs-5-to-6-migrate -p src/tsconfig.app.json

I'm running Node version 9.4.0 and .Net Core 2.1.200 on Windows 10 (1703) Enterprise.

Any ideas on how to fix this? Here is a full stack trace:

 ---> System.IO.EndOfStreamException: Attempted to read past the end of the stream.
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.SpaServices.AngularCli.AngularCliMiddleware.<StartAngularCliServerAsync>d__3.MoveNext()
   --- End of inner exception stack trace ---
   at Microsoft.AspNetCore.SpaServices.AngularCli.AngularCliMiddleware.<StartAngularCliServerAsync>d__3.MoveNext()
   --- End of inner exception stack trace ---
   at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)
   at Microsoft.AspNetCore.SpaServices.AngularCli.AngularCliMiddleware.<>c.<Attach>b__2_0(Task`1 task)
   at System.Threading.Tasks.ContinuationResultTaskFromResultTask`2.InnerInvoke()
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot)
   --- End of inner exception stack trace ---
   at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)
   at Microsoft.AspNetCore.SpaServices.Extensions.Util.TaskTimeoutExtensions.<WithTimeout>d__1`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.SpaServices.Extensions.Proxy.SpaProxy.<PerformProxyRequest>d__4.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.Builder.SpaProxyingExtensions.<>c__DisplayClass2_0.<<UseProxyToSpaDevelopmentServer>b__0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.Builder.RouterMiddleware.<Invoke>d__4.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.<Invoke>d__7.MoveNext()
---> (Inner Exception #0) System.AggregateException: One or more errors occurred. (The NPM script 'start' exited without indicating that the Angular CLI was listening for requests. The error output was: Unknown option: '--extractCss'

) ---> System.InvalidOperationException: The NPM script 'start' exited without indicating that the Angular CLI was listening for requests. The error output was: Unknown option: '--extractCss'

 ---> System.IO.EndOfStreamException: Attempted to read past the end of the stream.
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.SpaServices.AngularCli.AngularCliMiddleware.<StartAngularCliServerAsync>d__3.MoveNext()
   --- End of inner exception stack trace ---
   at Microsoft.AspNetCore.SpaServices.AngularCli.AngularCliMiddleware.<StartAngularCliServerAsync>d__3.MoveNext()
   --- End of inner exception stack trace ---
   at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)
   at Microsoft.AspNetCore.SpaServices.AngularCli.AngularCliMiddleware.<>c.<Attach>b__2_0(Task`1 task)
   at System.Threading.Tasks.ContinuationResultTaskFromResultTask`2.InnerInvoke()
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot)
---> (Inner Exception #0) System.InvalidOperationException: The NPM script 'start' exited without indicating that the Angular CLI was listening for requests. The error output was: Unknown option: '--extractCss'

 ---> System.IO.EndOfStreamException: Attempted to read past the end of the stream.
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.SpaServices.AngularCli.AngularCliMiddleware.<StartAngularCliServerAsync>d__3.MoveNext()
   --- End of inner exception stack trace ---
   at Microsoft.AspNetCore.SpaServices.AngularCli.AngularCliMiddleware.<StartAngularCliServerAsync>d__3.MoveNext()<---
<---

Answer 1

Try to do the following

1. Open a Powershell
2. Navigate to the clientapp directory
3. Run npm audit fix

This works for ReactJS & VueJS projects too.