Angular 9 "Error: This constructor was not compatible with Dependency Injection."

Question

This weird error, that I don't remember seeing pre-Ivy, has popped up in the setup of a new app created with the latest Angular 9 CLI. Looks like it could be a bug with Ivy? Any ideas on how to fix would be greatly appreciated.

Error result from ng test

Error: This constructor was not compatible with Dependency Injection.
    at Module.ɵɵinvalidFactory (http://localhost:9876/_karma_webpack_/node_modules/@angular/core/__ivy_ngcc__/fesm5/core.js:14150:1)
    at Object.Router_Factory [as factory] (http://localhost:9876/_karma_webpack_/node_modules/@angular/router/__ivy_ngcc__/fesm5/router.js:4404:67)
    at R3Injector.push../node_modules/@angular/core/__ivy_ngcc__/fesm5/core.js.R3Injector.hydrate (http://localhost:9876/_karma_webpack_/node_modules/@angular/core/__ivy_ngcc__/fesm5/core.js:11425:1)
    at R3Injector.push../node_modules/@angular/core/__ivy_ngcc__/fesm5/core.js.R3Injector.get (http://localhost:9876/_karma_webpack_/node_modules/@angular/core/__ivy_ngcc__/fesm5/core.js:11247:1)
    at injectInjectorOnly (http://localhost:9876/_karma_webpack_/node_modules/@angular/core/__ivy_ngcc__/fesm5/core.js:787:1)
    at ɵɵinject (http://localhost:9876/_karma_webpack_/node_modules/@angular/core/__ivy_ngcc__/fesm5/core.js:792:1)
    at Object.AuthService_Factory [as factory] (ng:///AuthService/ɵfac.js:5:39)
    at R3Injector.push../node_modules/@angular/core/__ivy_ngcc__/fesm5/core.js.R3Injector.hydrate (http://localhost:9876/_karma_webpack_/node_modules/@angular/core/__ivy_ngcc__/fesm5/core.js:11425:1)
    at R3Injector.push../node_modules/@angular/core/__ivy_ngcc__/fesm5/core.js.R3Injector.get (http://localhost:9876/_karma_webpack_/node_modules/@angular/core/__ivy_ngcc__/fesm5/core.js:11247:1)
    at NgModuleRef$1.push../node_modules/@angular/core/__ivy_ngcc__/fesm5/core.js.NgModuleRef$1.get (http://localhost:9876/_karma_webpack_/node_modules/@angular/core/__ivy_ngcc__/fesm5/core.js:24218:1)

Error: Expected undefined to be truthy.
    at <Jasmine>
    at UserContext.<anonymous> (http://localhost:9876/_karma_webpack_/src/app/shared/components/header/header.component.spec.ts:25:23)
    at ZoneDelegate.invoke (http://localhost:9876/_karma_webpack_/node_modules/zone.js/dist/zone.js:396:1)
    at ProxyZoneSpec.onInvoke (http://localhost:9876/_karma_webpack_/node_modules/zone.js/dist/zone-testing.js:305:1)

app.component.ts

import { Component, HostBinding } from '@angular/core';
import { AuthService, ScreenService, AppInfoService } from './shared/services';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.scss'],
})
export class AppComponent {
  @HostBinding('class') get getClass() {
    return Object.keys(this.screen.sizes)
      .filter(cl => this.screen.sizes[cl])
      .join(' ');
  }

  constructor(
    private authService: AuthService,
    private screen: ScreenService,
    public appInfo: AppInfoService,
  ) {}

  isAuthorized() {
    return this.authService.isLoggedIn;
  }
}

app.component.spec.ts

import { async, ComponentFixture, TestBed } from '@angular/core/testing';
import { Router } from '@angular/router';

import { AppComponent } from './app.component';
import { AuthService } from './shared/services';

describe('AppComponent', () => {
  let component: AppComponent;
  let fixture: ComponentFixture<AppComponent>;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [AppComponent],
      providers: [AuthService, Router],
    }).compileComponents();
  }));

  beforeEach(() => {
    fixture = TestBed.createComponent(AppComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  });

  it('should create', () => {
    expect(component).toBeTruthy();
  });
});

package.json dependencies

  "dependencies": {
    "@angular/animations": "~9.0.2",
    "@angular/cdk": "^8.0.0",
    "@angular/common": "~9.0.2",
    "@angular/compiler": "~9.0.2",
    "@angular/core": "~9.0.2",
    "@angular/forms": "~9.0.2",
    "@angular/platform-browser": "~9.0.2",
    "@angular/platform-browser-dynamic": "~9.0.2",
    "@angular/router": "~9.0.2",
    "devextreme": "latest",
    "devextreme-angular": "latest",
    "rxjs": "~6.5.4",
    "tslib": "^1.10.0",
    "zone.js": "~0.10.2"
  },
  "devDependencies": {
    "@angular-devkit/build-angular": "~0.900.3",
    "@angular/cli": "~9.0.3",
    "@angular/compiler-cli": "~9.0.2",
    "@angular/language-service": "~9.0.2",
    "@types/jasmine": "~3.5.0",
    "@types/jasminewd2": "~2.0.3",
    "@types/node": "^12.11.1",
    "codelyzer": "^5.1.2",
    "devextreme-cli": "latest",
    "devextreme-themebuilder": "latest",
    "husky": "^4.2.3",
    "jasmine-core": "~3.5.0",
    "jasmine-spec-reporter": "~4.2.1",
    "karma": "~4.3.0",
    "karma-chrome-launcher": "~3.1.0",
    "karma-coverage-istanbul-reporter": "~2.1.0",
    "karma-jasmine": "~2.0.1",
    "karma-jasmine-html-reporter": "^1.4.2",
    "prettier": "^1.19.1",
    "pretty-quick": "^2.0.1",
    "protractor": "~5.4.3",
    "ts-node": "~8.3.0",
    "tslint": "~5.18.0",
    "tslint-config-prettier": "^1.18.0",
    "typescript": "~3.7.5",
    "webpack-bundle-analyzer": "^3.6.0"
  }

NOTE: this error appeared after fixing NullInjectorError for both AuthService & Router.

Answer 1

You set a Router as provider in your test. That's not the way to do that.

You should import the RouterTestingModule in your test to be able to access it.

beforeEach(async(() => {
  TestBed.configureTestingModule({
    imports: [RouterTestingModule],
    declarations: [AppComponent],
    providers: [AuthService],
  }).compileComponents();
}));

I guess with ivy and/or angular 9, they declared the `providedIn` from the router service in such a way that you cannot provide it in another module anymore (which you should never do anyways :))

---

Background info:

Looking at the source code, you can see they inject the router in a special way using a factory. The router class itself is just a normal class with no @Injectable() decorator.

Answer 2

Another source of this error (not related to the OP's question) can be when you have a constructor param with a default arg such as:

constructor(someProp: string = 'propVal') {
    this.someProp = someProp;
}

You can resolve it by doing this instead:

constructor(@Inject('propVal') @Optional() someProp: string) {
    this.someProp = someProp;
}

Answer 3

This error can also be produced if you accidentally try to inject an interface instead of a service, lol.

example.interface.ts

export interface ExampleInterface {
  id: string
}

example.service.ts

import { Injectable } from '@angular/core'

@Injectable({
  providedIn: 'root'
})
export class ExampleService {
  constructor() { }
}

dependent.service.ts

import { Injectable } from '@angular/core'

@Injectable({
  providedIn: 'root'
})
export class DependentService {
  constructor(
    private example: ExampleInterface // This is the error; should be ExampleService
  ) { }
}

Answer 4

If angular build was in --watch mode, try to restart it.