Fixed it by opting out of Ivy as per documentation.

https://angular.io/guide/ivy

Change tsconfig.app.json to opt out of Ivy.

"enableIvy": false

Your module is not yet loaded by the Angular Server in node ng serve, so restart your server so the server loads the module that you just added in @NgModule app.module.ts

This works for me:

1) Stop the ng server

2) Reinstall your package

npm install your-package-name

3) Run all again

ng serve

This issue will be fixed by adding the postinstall script below in your package.json.

It will be run after a npm install.

"scripts": {
   "postinstall": "ngcc"
}

Post adding the above code, run npm install

This works for me when upgrading to Angular 9+

This error shows when you add component declaration in imports: [] instead of declarations: [], e.g:

declarations: [
  AppComponent,
],
imports: [
  BrowserModule,
  AppRoutingModule,
  SomeComponent <-----------wrong
],

npm cache clean --force -> cleaning the cache maybe solve the issue.

I have tested all the answers here but non of them worked for me. So I decided to change angular.js file. there is a aot option there which is true. then I altered that to the false and the error vanished!

"options": {
            "outputPath": "dist/DateMeUI",
            "index": "src/index.html",
            "main": "src/main.ts",
            "polyfills": "src/polyfills.ts",
            "tsConfig": "tsconfig.app.json",
            "aot": false, // here you have to change
            "assets": [
              "src/favicon.ico",
              "src/assets"
            ],
            "styles": [
              "src/styles.css"
            ],
            "scripts": []
          },

However, I got that there is 'tsconfig.app.json' which I couldn't find that in my project(maybe you have to add this manually ) by this file you can set the "enableIvy": false as others mention to it. tsconfig.app.json

I got this error when I made the bonehead mistake of importing MatSnackBar instead of MatSnackBarModule in app.module.ts.

Work for me

angular.json

"aot": false

This works for me

1. Stop the ng server(ctrl+c)

2. Run Again

   npm start / ng serve --open
   

i simply change my import from import from { AngularFirestore} from '@angular/fire/firestore'; to import { AngularFirestoreModule } from '@angular/fire/firestore';

and it's working fine

Just go to your tsconfig.app.json in your project and remove all from it

and copy below code and paste it. It will solve your issue :)

/* To learn more about this file see: https://angular.io/config/tsconfig. */
{
  "extends": "./tsconfig.json",
  "compilerOptions": {
    "outDir": "./out-tsc/app",
    "types": [],
  },

  "files": [
    "src/main.ts",
    "src/polyfills.ts"
  ],
  "include": [
    "src/**/*.d.ts"
  ],
  "angularCompilerOptions": {
    "enableIvy": false
  }
}

I made a mistake by adding a service into imports array instead of providers array.

@NgModule({
  imports: [
    MyService // wrong here
  ],
  providers: [
    MyService // should add here
  ]
})
export class AppModule { }

Angular says you need to add Injectables into providers array.

I have faced the same issue in Ubuntu because the Angular app directory was having root permission. Changing the ownership to the local user solved the issue for me.

$ sudo -i
$ chown -R <username>:<group> <ANGULAR_APP>
$ exit 
$ cd <ANGULAR_APP>
$ ng serve

For me I was working under Ubuntu

The error disappeared if I use sudo with ng

sudo ng build
sudo ng serve

A better solution is to grant the current user the needed permissions on the current folder using the following command:

sudo chown -R `whoami` ./

Doing so will let you run ng commands without sudo.

This can also occur when using the wrong import (for example when using autoimport). let's take the MatTimePickerModule as an example. This will give an error message that is similar to the one described in the question:

import { NgxMatTimepickerModule } from '@angular-material-components/datetime-picker/lib/timepicker.module';

This should instead be

import { NgxMatTimepickerModule } from '@angular-material-components/datetime-picker';

Sometimes when you change/update @NgModule in your project, projects get compiled but changes doesn't get reflect. So, restart once to get expected results if you not get it. ng serve

What fixed it for me was matching the version of angular material & adapter to the lowest version of another angular module. Then reinstalled & re-ran.

    "@angular-devkit/schematics": "^10.1.2",
    "@angular/animations": "^10.1.2",
    "@angular/cdk": "^10.2.1",
    "@angular/common": "10.1.2",
    "@angular/compiler": "10.1.2",
    "@angular/core": "10.1.2",
    "@angular/forms": "10.1.2",
    "@angular/localize": "^10.1.2",
    "@angular/material": "^10.2.1",
    "@angular/material-moment-adapter": "^10.2.1",
    "@angular/platform-browser": "10.1.2",
    "@angular/platform-browser-dynamic": "10.1.2",
    "@angular/router": "10.1.2",

As you can see my cdk was 10.2.1, and my material was also 10.2.1. I saw the lowest version used was 10.1.2, so i changed the versions:

    "@angular/material": "^10.1.2", (was 10.2.1)
    "@angular/material-moment-adapter": "^10.1.2", (was 10.2.1)

to 10.1.2, ran "npm install" and then "ng serve", and it compiled successfully.

In my case I got this solved by setting "strictTemplates" back to false in tsconfig.json

{
  "compilerOptions": {
    // ...
  },
  "angularCompilerOptions": {
    "strictTemplates": false
  }
}

I had previously set this to true to prevent a VStudio pop-up from showing:

1. App.Module.ts

   You can solve the error by adding the injectables in Provider not imports or declarations.

2. Inside Service.ts

   Add @injectable over the class

ex:

@Injectable()
 export class WebApiService {   }

even if you give space might not work

ex:

@Injectable()


export class WebApiService {    }

In my case the problem was calling .forRoot() from some child modules that were meant to be re-used.

I was importing mat-list. My mistake was using the following:

import { MatList } from "@angular/material/list";
@NgModule({
  exports: [
    MatList,
  ]
})

I forgot to append 'Module' suffix to the import and export declaration. The following fixed the problem:

import { MatListModule } from "@angular/material/list";
@NgModule({
  exports: [        
    MatListModule,
  ]
})

It also happens when you import some mat components which is not used anywhere in your components.

• if you have all mat components imported in you app.module.ts you have imported some mat components and you have not used any of the components in imports and exports arrays in app.module.ts means no issues no errors will throw works fine.

• if you create feature module for that let say by ng g m material this will create material.module.ts filename.

• now we have to copy all mat import statements to newly created feature module before copying keep in mind is any import statements grayed out or not(some indication IDE shows this name is not used). if grayed out means you have to remove those names then copy and paste it to MaterialModule imports and exports array. that's solve.

In my case, the problem was with the latest node. I was dockerizing the Angular app and using the latest node version like FROM node:latest as build

To make it work use Angular supported node versions like FROM node:14.17.4

it can be occurs when you import a module that you already installed, but one ore more of its dependencies are missing

I faced issue on Angular 12 and the issue is my colleague defined the component in page module and as well as the common module we use globally in project.

Removed from globally file module, issue resolved.

On My Case

My mistake: I wrote

import { MatPaginator } from '@angular/material/paginator';

instead of

import { MatPaginatorModule } from '@angular/material/paginator';

in my module.

I got this error while making a shared directive. Now Initially it got into declarations array of the app module (by default after I ran command with cli).

I had it into shared module declarations array and exports array. Now as soon as I removed it from app.module.ts file the issue got resolved.

The issue was it was declared inside 2 modules (shared and app.module). Removed from the app.module and voila!

If you run npm install or yarn install with root account and run ng serve with a non-root account, you will encounter this issue.

Workaround: start server with root account as well

try to clear cache

1. npm cache clean --force
2. npm install

I was trying to add a custom pipe to my shared module and I've added it in import and export. That's why it caused this issue.

I solved this issue by adding my custom pipe into declarations:[], exports:[] and providers:[].

I solved this issue by following code :

@NgModule({

 declarations: [
   myCustomPipe,
 ],

 exports: [
   myCustomPipe,
 ],

 providers: [
  myCustomPipe,
 ]

})

I don't know why but the only way I could solve it was to:

1. Import the module instead of the component
2. Match the folder name /my-component-y/ with MyComponentY.ts, I had /component-y/ and MyComponentY.ts

The root components are lazy loaded since it's for a mulitsite if that makes any difference.

Best solution is to use React/Next.js instead though of this old hacky framework.