source: https://www.reddit.com/r/learnprogramming/comments/9735g2/angular_6_typescript_read_content_from_file_in/

import { HttpClient } from '@angular/common/http';
 
…
 
 constructor(
    private http: HttpClient
  ) {}
 
…
 
this.http.get('assets/test.txt', {responseType: 'text'})
        .subscribe(data => console.log(data));