I'm new to Angular 6 and i'm having trouble on how i can add objects into observable in a service.

i have this observable

 getContacts()
 return this.contact = 
 this.http.get('https://jsonplaceholder.typicode.com/users');
 

and i need to add an item into that observable via another function

addContact(item)
 //observable insertion goes here.

Here is my full service code

export class ContactService 

contact;
details;

constructor(private http: HttpClient) 

getContacts()
 return this.contact = 
 this.http.get('https://jsonplaceholder.typicode.com/users');


addContact(contactName: string, contactPhone: string)

If this.contacts is an Observable of list of objects (contacts: Observable<Items>) and you want to make some changes to that list, you can simply use map like this:

import map from 'rxjs/operators';

this.contacts.pipe(map(usersList => 
 usersList.push(newItem);
 return usersList;
));

But if you want to make another request to the server and merge this lists, you can use forkJoin like this:

import forkJoin from 'rxjs';

forkJoin(
 this.contacts,
 this.http.get('https://jsonplaceholder.typicode.com/other_users');
).pipe(
 map(data => 
 const currentResult = data[0];
 const pastResult = data[1];
 // ...
 
));

Update

Based on the your comment for more details, you don't need to do anything with observables. You need is something like this:

In your contacts.service.ts:

getContacts()
 return this.contact = this.http.get('https://jsonplaceholder.typicode.com/users');

In your contacts.component.ts`:

contacts: any = ;
ngOnInit() 
 this.contactsService.getContacts.subscribe(data => this.contacts = data);


addContact(item) 
 this.contacts.push(item);

But if you really want to have your contacts list as an Observable, you should use Subject.

In your contacts.service.ts:

$contactsChange = new Subject<any>();
private contactsList = ;
getContacts()
 return this.contact = this.http.get('https://jsonplaceholder.typicode.com/users').pipe(map(data => 
 this.contactsList = data;
 this.$contactsChange.next(this.contactsList);
 ));


addContact(item) 
 this.contactsList.push(item);
 this.$contactsChange.next(this.contactsList);

In your contacts.component.ts`:

contacts: any = ;
ngOnInit() 
 this.contactsService.getContacts.subscribe(data => this.contacts = data);
 this.contactsService.$contactsChange.subscribe(data => this.contacts = data);

The addContact () method is where you subscribe to the observable getContacts():

getContacts(): Observable<any> 
 return this.contact = 
 this.http.get('https://jsonplaceholder.typicode.com/users');

At the time of subscription is when the call is triggered:

addContact()
 let cont: Observable<contactModel>;
 cont = this.getContacts();
 prueba.finally(() => 
 console.log('Finally callback')
 )
 cont.subscribe(res => 
 console.log('at the time of subscription is when the call is triggered')
 let resp: contactModel;
 resp = res.json() as contactModel; 
 );