If '<selector>' is an Angular component, then verify that it is part of this module

Your MyComponentComponent should be in MyComponentModule.

And in MyComponentModule, you should place the MyComponentComponent inside the "exports".

Something like this, see code below.

@NgModule({
   imports: [],
   exports: [MyComponentComponent],
   declarations: [MyComponentComponent],
   providers: [],
})

export class MyComponentModule {
}

and place the MyComponentModule in the imports in app.module.ts like this (see code below).

import { MyComponentModule } from 'your/file/path';

@NgModule({
   imports: [MyComponentModule]
   declarations: [AppComponent],
   providers: [],
   bootstrap: [AppComponent]
})

export class AppModule {}

After doing so, the selector of your component can now be recognized by the app.

You can learn more about it here: https://angular-2-training-book.rangle.io/handout/modules/feature-modules.html

Cheers!

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Maybe This is for name of html tag component

You use in html something like this <mycomponent></mycomponent>

You must use this <app-mycomponent></app-mycomponent>

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are you importing it in your app.module.ts like so and remove the directives bit:-

@NgModule({
    bootstrap: [AppComponent],
    imports: [MyComponentModule],// or whatever the name of the module is that declares your component.

    declarations: [AppComponent],
    providers: []
})
export class AppModule {}

Your MyComponentModule should be like this:-

@NgModule({
    imports: [],
    exports: [MyComponentComponent],
    declarations: [MyComponentComponent],
    providers: [],
})
export class MyComponentModule {
}

---

In my case I was writing unit tests for a component that uses sub-components, and I was writing tests to make sure those subcomponents were in the template:

it('should include the interview selection subview', () => {
    expect(fixture.debugElement.query(By.css('app-interview')))
    .toBeTruthy()  
  }); 

I didn't get an error, but a warning:

WARN: ''app-interview' is not a known element: If 'app-interview' is an Angular component, then verify that it is part of this module. WARN: ''app-interview' is not a known element: If 'app-interview' is an Angular component, then verify that it is part of this module. If 'app-interview' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.'

Also, the subcomponent did not show inside the browser during testing.

I used ng g c newcomponent to generate all the components, so they were already declared in the appmodule, but not the test module that for the component I was spec'ing.

beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [ EditorComponent,
        InterviewComponent]
    })
    .compileComponents();
  }));

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Check your selector in your filename.component.ts

Using the tag in various html files I would say

<my-first-component></my-first-component>

Should be

<app-my-first-component></app-my-first-component>

Example

@Component({
  selector: 'app-my-first-component',
  templateUrl: './my-first-component.component.html',
  styleUrls: ['./my-first-component.component.scss']
})

---

Declare your MyComponentComponent in MyComponentModule Add your MyComponentComponent to exports attribute of MyComponentModule

mycomponentModule.ts

@NgModule({
   imports: [],
   exports: [MyComponentComponent],
   declarations: [MyComponentComponent],
   providers: [],
})

export class MyComponentModule {
}

Add your MyComponentModule to your AppModule imports attribute

app.module.ts

    @NgModule({
       imports: [MyComponentModule]
       declarations: [AppComponent],
       providers: [],
       bootstrap: [AppComponent]
    })
    export class AppModule {} 

Important If your still have that error, Stop your server ctrl+c from terminal, and run it again ng serve -o

---

Go to the tsconfig.json file. write this code under angularCompilerOption:

 "angularCompilerOptions": {
     "fullTemplateTypeCheck": true,
     "strictInjectionParameters": true,
     **"enableIvy": false**
 }

---

Had the same issue, found that the template component tags worked with <app-[component-name]></app-[component-name]>. So, if your component is called mycomponent.component.ts:

@Component({
  selector: 'my-app',
  template: `
    <h1>Hello {{name}}</h1>
    <h4>Something</h4>
    <app-mycomponent></app-mycomponent>
  `,

---

You must declare your MyComponentComponent in the same module of your AppComponent.

import { AppComponent } from '...';
import { MyComponentComponent } from '...';

@NgModule({
   declarations: [ AppComponent, MyComponentComponent ],
   bootstrap: [ AppComponent ]
})
export class AppModule {}

---

In my case I had a component in a Shared module.

The component was loading and worked well but typescript was highlighting the html tag with red line and showed this error message.

Inside this component, I noticed I didn't import a rxjs operator.

import {map} from 'rxjs/operators';

When I added this import the error message disappeared.

Check all imports inside the component.

Hope it helps someone.

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Check which module the parent component is being declared in...

If your parent component is defined in the shared module, so must your child module.

The parent component could be declared in a shared module and not the module that is logical based on the file directory structure / naming, even the Angular CLI added it into the wrong module in my case.

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I am using Angular v11 and was facing this error while trying to lazy load a component (await import('./my-component.component')) and even if import and export were correctly set.

I finally figured out that the solution was deleting the separate dedicated module's file and move the module content inside the component file itself.

rm -r my-component.module.ts

and add module inside my-component.ts (same file)

@Component({
  selector: 'app-my-component',
  templateUrl: './my-component.page.html',
  styleUrls: ['./my-component.page.scss'],
})
export class MyComponent {
}

@NgModule({
  imports: [CommonModule],
  declarations: [MyComponent],
})
export class MyComponentModule {}

---

Hope you are having app.module.ts. In your app.module.ts add below line-

 exports: [myComponentComponent],

Like this:

import { NgModule, Renderer } from '@angular/core';
import { HeaderComponent } from './headerComponent/header.component';
import { HeaderMainComponent } from './component';
import { RouterModule } from '@angular/router';

@NgModule({
    declarations: [
        HeaderMainComponent,
        HeaderComponent
    ],
    imports: [
        RouterModule,
    ],
    providers: [],
    bootstrap: [HeaderMainComponent],
    exports: [HeaderComponent],
})
export class HeaderModule { }

---

In your components.module.ts you should import IonicModule like this:

import { IonicModule } from '@ionic/angular';

Then import IonicModule like this:

  imports: [
    CommonModule,
    IonicModule
  ],

so your components.module.ts will be like this:

import { CommonModule } from '@angular/common';
import {PostComponent} from './post/post.component'
import { IonicModule } from '@ionic/angular';

@NgModule({
  declarations: [PostComponent],
  imports: [
    CommonModule,
    IonicModule
  ],
  exports: [PostComponent]
})
export class ComponentsModule { }```

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Don't export **default** class MyComponentComponent!

Related issue that might fall under the title, if not the specific question:

I accidentally did a...

export default class MyComponentComponent {

... and that screwed things up too.

Why? VS Code added the import to my module when I put it into declarations, but instead of...

import { MyComponentComponent } from '...';

it had

import MyComponentComponent from '...';

And that didn't map up downstream, assumedly since it wasn't "really" named anywhere with the default import.

export class MyComponentComponent {

No default. Profit.

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This might be late ,but i got the same issue but I rebuild(ng serve) the project and the error was gone

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The above error is produced from Angular 9 onwards as well. This book provides a solution.

"The warning suggests CUSTOM_ELEMENTS_SCHEMA, but the elements in question are not Web Components. We want Angular to simply ignore the elements. Therefore we use the NO_ERRORS_SCHEMA, “a schema that allows any property on any element”. Adding schemas: [NO_ERRORS_SCHEMA] to your respective .spec file removes the error.

await TestBed.configureTestingModule({
  declarations: [MyComponent],
  schemas: [NO_ERRORS_SCHEMA],
}).compileComponents();

---

I had a similar Problem, but none of the mentioned solutions worked. In the end i realized i have a routing problem:

I thought if i specify my component in the app-routing.module like so:

import { NgModule } from '@angular/core';
import { RouterModule, Routes } from '@angular/router';
import { MainComponent } from './pages/main/main.component';

const routes: Routes = [
  {
    path: '', 
    component: MainComponent
  },
]

@NgModule({
  imports: [RouterModule.forRoot(routes)],
  exports: [RouterModule]
})
export class AppRoutingModule { }

i would not have to import the MainModule in my AppModule, which is wrong since here only the component gets imported. Any other components declared in MainModule will not be visible which results in the error message you described.

Solution 1: Import the declaring module Solution 2: Lazyload the component like so:

const routes: Routes = [
{
    path: '', loadChildren: () => import('path_to_your_declaringModule').then(m => m.declaringModule)},
}

This works since the whole module gets imported here.

I realize you do not use routing in your example, just posting this for any other person that might use routing and stumbles across this question in search for a solution, like i did.

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