Angular 2 'component' is not a known element

Question

I\'m trying to use a component I created inside the AppModule in other modules. I get the following error though:

\"Uncaught (in promise): Error: Temp

Answer 1

Supposedly you have a component:

product-list.component.ts:

import { Component } from '@angular/core';
    
    @Component({
        selector: 'pm-products',  
        templateUrl: './product-list.component.html'
    })
    
    
    export class ProductListComponent {
      pageTitle: string = 'product list';
    }

And you get this error:

ERROR in src/app/app.component.ts:6:3 - error NG8001: 'pm-products' is not a known element:

1. If 'pm-products' is an Angular component, then verify that it is part of this module.

app.component.ts:

import { Component } from "@angular/core";
@Component({
  selector: 'pm-root', // 'pm-root'
  template: `
  <div><h1>{{pageTitle}}</h1>
  <pm-products></pm-products> // not a known element ?
  </div>
  `
})
export class AppComponent {
  pageTitle: string = 'Acme Product Management';
}

Make sure you import the component:

app.module.ts:

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';

import { AppComponent } from './app.component';

// --> add this import (you can click on the light bulb in the squiggly line in VS Code)
import { ProductListComponent } from './products/product-list.component'; 

@NgModule({
  declarations: [
    AppComponent,
    ProductListComponent // --> Add this line here

  ],
  imports: [
    BrowserModule
  ],
  bootstrap: [AppComponent],


})
export class AppModule { }

Answer 2

I got the same issue, and it was happening because of different feature module included this component by mistake. When removed it from the other feature, it worked!

Answer 3

A lot of answers/comments mention components defined in other modules, or that you have to import/declare the component (that you want to use in another component) in its/their containing module.

But in the simple case where you want to use component A from component B when both are defined in the same module, you have to declare both components in the containing module for B to see A, and not only A.

I.e. in my-module.module.ts

import { AComponent } from "./A/A.component";
import { BComponent } from "./B/B.component";

@NgModule({
  declarations: [
    AComponent,   // This is the one that we naturally think of adding ..
    BComponent,   // .. but forget this one and you get a "**'AComponent'** 
                  // is not a known element" error.
  ],
})