Angular5 httpClient get:Cannot read property 'toLowerCase' of undefined

Question

I am trying to get a list of Users from an API but I get the following error:

TypeError: Cannot read property 'toLowerCase' of undefined
at HttpXsrfInterceptor.intercept (http.js:2482)
at HttpInterceptorHandler.handle (http.js:1796)
at HttpInterceptingHandler.handle (http.js:2547)
at MergeMapSubscriber.eval [as project] (http.js:1466)
at MergeMapSubscriber._tryNext (mergeMap.js:128)
at MergeMapSubscriber._next (mergeMap.js:118)
at MergeMapSubscriber.Subscriber.next (Subscriber.js:92)
at ScalarObservable._subscribe (ScalarObservable.js:51)
at ScalarObservable.Observable._trySubscribe (Observable.js:172)
at ScalarObservable.Observable.subscribe (Observable.js:160)

I have a login component that calls the homeService.getUsers() which uses HttpClient to retrieve the users but the http request never reaches the server.

login.component.ts:

import { Component, OnInit } from '@angular/core';

import { HomeService } from '../service/home.service';
import { User } from '../domain/user';

@Component({
  selector: 'app-login',
  templateUrl: './login.component.html',
  styleUrls: ['./login.component.scss']
})
export class LoginComponent implements OnInit {

  user: User = {
      id: undefined,
      userName: undefined,
      password: undefined
  }; 
  users: User[];

  constructor(
    private homeService: HomeService
  ) { }

  ngOnInit() {
    this.getUsers();
  }

  getUsers(): void {
    this.homeService.getUsers()
    .subscribe(users => this.users = users);
  }
}

Home.service:

import { Injectable } from '@angular/core';
import { HttpClient, HttpHeaders, HttpParams } from '@angular/common/http';

import { Observable } from 'rxjs/Observable';
import { of } from 'rxjs/observable/of';
import { catchError, map, tap } from 'rxjs/operators';

import { User } from '../domain/user';
import { MessageService } from '../service/message.service';

const httpOptions = {
  headers: new HttpHeaders({ 'Content-Type': 'application/json' })
};

@Injectable()
export class HomeService {

  private usersUrl: 'http://localhost:8080/users';

  constructor(
    private http: HttpClient,
    private messageService: MessageService
  ) { }

  getUsers (): Observable<User[]> {
    return this.http.get<User[]>(this.usersUrl)
      .pipe(
        tap(users => this.log(`fetched users`)),
        catchError(this.handleError('getUsers', []))
      );
  }

  /**
  * Handle Http operation that failed.
  * Let the app continue.
  * @param operation - name of the operation that failed
  * @param result - optional value to return as the observable result
  */
  private handleError<T> (operation = 'operation', result?: T) {
    return (error: any): Observable<T> => {

      // TODO: send the error to remote logging infrastructure
      console.error(error); // log to console instead

      // TODO: better job of transforming error for user consumption
      this.log(`${operation} failed: ${error.message}`);

      // Let the app keep running by returning an empty result.
      return of(result as T);
    };
  }

  private log(message: string) {
    this.messageService.add(message);
  }

}

and the app.module:

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { FormsModule } from '@angular/forms';
import { RouterModule, Routes } from '@angular/router';
import { HttpClientModule } from '@angular/common/http';
import { HttpClientXsrfModule } from '@angular/common/http';

import { AppComponent } from './app.component';
import { HomeComponent } from './home/home.component';
import { HomeService } from './service/home.service';
import { MessagesComponent } from './messages/messages.component';
import { MessageService } from './service/message.service';
import { LoginComponent } from './login/login.component';
import { RegisterComponent } from './register/register.component';

@NgModule({
  declarations: [
    AppComponent,
    HomeComponent,
    LoginComponent,
    RegisterComponent,
    MessagesComponent
  ],
  imports: [
    BrowserModule,
    FormsModule,
    HttpClientModule,
    HttpClientXsrfModule.withOptions({
      cookieName: 'My-Xsrf-Cookie',
      headerName: 'My-Xsrf-Header',
    })
  ],
  providers: [HomeService, MessageService],
  bootstrap: [AppComponent]
})
export class AppModule { }

I can see the error message displayed in the logging, so it seems like an error from the HttpClient. But I can't figure out why it is failing before sending the Http request to the server.

Answer 1

I got the same issue. The problem was that I had declared the url, but when doing the httpget, i realized that the url was not assigned with any value:

Probable case: Example: private yourUrl: string;

and in your http call: return this.http.get(this.yourUrl, {headers : this.headers})