// RxJS v6+
import { throwError } from 'rxjs';
​
//emits an error with specified value on subscription
const source = throwError('This is an error!');
//output: 'Error: This is an error!'
const subscribe = source.subscribe({
  next: val => console.log(val),
  complete: () => console.log('Complete!'),
  error: val => console.log(`Error: ${val}`)
});