Angular2 RC6: '<component> is not a known element'

I received this error when I imported Module A into Module B, and then tried to use a component from Module A in Module B.

The solution is to declare that component in the exports array.

@NgModule({
  declarations: [
    MyComponent
  ],
  exports: [
    MyComponent
  ]
})
export class ModuleA {}

@NgModule({
  imports: [
    ModuleA
  ]
})
export class ModuleB {}

I fixed it with help of Sanket's answer and the comments.

What you couldn't know and was not apparent in the Error Message is: I imported the PlannerComponent as a @NgModule.declaration in my App Module (= RootModule).

The error was fixed by importing the PlannerModule as @NgModule.imports.

Before:

@NgModule({
  declarations: [
    AppComponent,
    PlannerComponent,
    ProfilAreaComponent,
    HeaderAreaComponent,
    NavbarAreaComponent,
    GraphAreaComponent,
    EreignisbarAreaComponent
  ],
  imports: [
    BrowserModule,
    RouterModule.forRoot(routeConfig),
    PlannerModule
  ],
  bootstrap: [AppComponent]
})
export class AppModule {

After:

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    RouterModule.forRoot(routeConfig),
    PlannerModule
  ],
  bootstrap: [AppComponent]
})
export class AppModule {
}

Thanks for your help :)

If you have used the Webclipse automatically generated component definition you may find that the selector name has 'app-' prepended to it. Apparently this is a new convention when declaring sub-components of a main app component. Check how your selector has been defined in your component if you have used 'new' - 'component' to create it in Angular IDE. So instead of putting

<header-area></header-area>

you may need

<app-header-area></app-header-area>

I fetch same problem for <flash-messages></flash-messages> with angular 5.

You just need add below lines in app.module.ts file

import { ---, CUSTOM_ELEMENTS_SCHEMA } from '@angular/core';
import { FlashMessageModule } from "angular-flash-message";


@NgModule({
  ---------------
  imports: [
    FlashMessageModule,
    ------------------         
  ], 
  -----------------
  schemas: [ CUSTOM_ELEMENTS_SCHEMA ]
  ------------
})

NB: I am using this one for message flash-messages

In your planner component, you must be missing import HeaderAreaComponent like this-

import { HeaderAreaComponent } from '../header-area.component'; 
//change path according your project

Also, make sure - All the components and pipes must be declared via an NgModule.

See if this helps.

I was facing this issue on Angular 7 and the problem was after creating the module, I did not perform ng build. So I performed -

ng build

ng serve

and it worked.

The error coming in unit test, when component is out of <router-outlet> in main app page. so should define the component in test file like below.

<app-header></app-header>
<router-outlet></router-outlet>

and then needs to add in spec.ts file as below.

import { HeaderComponent } from './header/header.component';

describe('AppComponent', () => {
  beforeEach(async(() => {
    TestBed.configureTestingModule({
      imports: [
        RouterTestingModule
      ],
      declarations: [
        App`enter code here`Component,
        HeaderComponent <------------------------
      ],
    }).compileComponents();
  }));
});

Another possible cause of having the same error message is a mismatch between tag name and selector name. For this case:

<header-area></header-area> tag name must exactly match 'header-area' from the component declaration:

@Component({
  selector: 'header-area',

I had the same problem and i fixed by adding the component (MyComponentToUse) in exports array in the module where my component was declared (ModuleLower). Then i import ModuleLower in ModuleHigher, so i can reuse now my component ( MyComponentToUse) in the ModuleLower and the ModuleHigher

            @NgModule({
              declarations: [
                MyComponentToUse
              ],
              exports: [
                MyComponentToUse
              ]
            })
            export class ModuleLower {}


            @NgModule({
              imports: [
                ModuleLower
              ]
            })
            export class ModuleHigher {} 

I had the same issue with angular RC.6 for some reason it doesn't allow passing component to other component using directives as component decorator to the parent component

But it if you import the child component via app module and add it in the declaration array the error goes away. There are no much explanation to why this is an issue with angular rc.6

When I had this problem, it was because I used 'templateUrl' instead of just 'template' in the decorator, since I use webpack and need to use require in it. Just be careful with the decorator name, in my case I generated the boilerplate code using a snippet, the decorator was created as:

@Component({
  selector: '',
  templateUrl: 'PATH_TO_TEMPLATE'
})

but for webpack the decorator should be just 'template' NOT 'templateUrl', like so:

@Component({
  selector: '',
  template: require('PATH_TO_TEMPLATE')
})

changing this solved the problem for me.

wanna know more about the two methods? read this medium post about template vs templateUrl

I got this error when I had a filename and class exported mismatch:

filename: list.component.ts

class exported: ListStudentsComponent

Changing from ListStudentsComponent to ListComponent fixed my issue.

I ran across this exact problem. Failed: Template parse errors: 'app-login' is not a known element... with ng test. I tried all of the above replies: nothing worked.

NG TEST SOLUTION:

Angular 2 Karma Test 'component-name' is not a known element

<= I added declarations for the offending components into beforEach(.. declarations[]) to app.component.spec.ts.

EXAMPLE app.component.spec.ts

...
import { LoginComponent } from './login/login.component';
...
describe('AppComponent', () => {
  beforeEach(async(() => {
    TestBed.configureTestingModule({
      imports: [
        ...
      ],
      declarations: [
        AppComponent,
        LoginComponent
      ],
    }).compileComponents();
  ...

A newbie mistake was generating the same error message in my case.

The app-root tag wasn't present in index.html

For me path for templateUrl was not correct

I was using

shopping-list-edit.component.html

Whereas it should have been

./shopping-list-edit.component.html

Silly mistake but happens when starting out. Hope that helps somebody in distress.

I had the same issue with Angular 7 when I am going to refine the test module by declaring the test component. Just added schemas: [ CUSTOM_ELEMENTS_SCHEMA ] as follows and error was solved.

TestBed.configureTestingModule({
  imports: [ReactiveFormsModule, FormsModule],
  declarations: [AddNewRestaurantComponent],
  schemas: [ CUSTOM_ELEMENTS_SCHEMA ]
});

For future problems. If you think you followed all the good answers and yet, the problem is there.

Try turning the server off and on.

I had the same problem, followed all the steps, couldn't solve it. Turn off, on and it was fixed.

OnInit was automatically implemented on my class while using the ng new ... key phrase on angular CLI to generate the new component. So after I removed the implementation and removed the empty method that was generated, the problem is resolved.

Ok, let me give the details of code, how to use other module's component.

For example, I have M2 module, M2 module have comp23 component and comp2 component, Now I want to use comp23 and comp2 in app.module, here is how:

this is app.module.ts, see my comment,

 // import this module's ALL component, but not other module's component, only this module
  import { AppComponent } from './app.component';
  import { Comp1Component } from './comp1/comp1.component';

  // import all other module,
 import { SwModule } from './sw/sw.module';
 import { Sw1Module } from './sw1/sw1.module';
 import { M2Module } from './m2/m2.module';

   import { CustomerDashboardModule } from './customer-dashboard/customer-dashboard.module';


 @NgModule({

    // declare only this module's all component, not other module component.  

declarations: [
AppComponent,
Comp1Component,


 ],

 // imports all other module only.
imports: [
BrowserModule,
SwModule,
Sw1Module,
M2Module,
CustomerDashboardModule // add the feature module here
],
 providers: [],
 bootstrap: [AppComponent]
})
export class AppModule { }

this is m2 module:

   import { NgModule } from '@angular/core';
   import { CommonModule } from '@angular/common';

   // must import this module's all component file
   import { Comp2Component } from './comp2/comp2.component';
   import { Comp23Component } from './comp23/comp23.component';

   @NgModule({

   // import all other module here.
     imports: [
       CommonModule
     ],

    // declare only this module's child component. 
     declarations: [Comp2Component, Comp23Component],

   // for other module to use these component, must exports
     exports: [Comp2Component, Comp23Component]
   })
   export class M2Module { }

My commend in code explain what you need to do here.

now in app.component.html, you can use

  <app-comp23></app-comp23>

follow angular doc sample import modul

Late answer for the thread, but I'm sure there's more people that can use this information explained in another perspective.

In Ionic, custom angular components are organized under a separate module called ComponentsModule. When the first component is generated using ionic generate component, along with the component, ionic generates the ComponentsModule. Any subsequent components gets added to the same module, rightly so.

Here's a sample ComponentsModule

import { NgModule } from '@angular/core';
import { CustomAngularComponent } from './custom/custom-angular-component';
import { IonicModule } from 'ionic-angular';
@NgModule({
    declarations: [CustomAngularComponent],
    imports: [IonicModule],
    exports: [CustomAngularComponent],
    entryComponents:[

      ]
})
export class ComponentsModule {}

To use the ComponentsModule in the app, like any other angular modules, the ComponentsModules needs to be imported to the AppModule. ionic generate component (v 4.12) does not add this step, so this has to be added manually.

Excerpt of AppModule:

@NgModule({
  declarations: [
    //declaration
  ],
  imports: [
    //other modules 
    ComponentsModule,
  ],
  bootstrap: [IonicApp],
  entryComponents: [
    //ionic pages
  ],
  providers: [
    StatusBar,
    SplashScreen,
    {provide: ErrorHandler, useClass: IonicErrorHandler},
    //other providers
  ]
})
export class AppModule {}

HUMAN ERROR - DON'T BE MISLED BY THE ERROR MESSAGE.

Why I got misled: The component I wanted to consume (ComponentA) was correctly declared in it's module (ModuleA). It was correctly exported there, too. The module (ModuleB) of the component (ComponentB) I am working in, had the import for ModuleA correctly specified. However, because of the error message being < component-a-selector > is not a known element', my entire focus was in thinking that it was a problem with ModuleA/ComponentA as that is what the error message contained; I didn't think to look at the component I was trying to consume it from. I followed every single post in every threat about this, but was ultimately missing one vital step:

What fixed it for me: frot.io's answer prompted me to check my app.module.ts import list and the component I was working in (ComponentB) was not included!

When you are declaring components in one module, exporting them, then using them in another module, you have to make sure that the module with the exports is also imported in app module. :)