Angular2: convert array to Observable

import { of } from 'rxjs';
    
return of(this.contacts);

You're right there. If you already have the data in memory, you can use of observable (equivalent of return/just in RxJS 4).

getContacts() {

    if(this.contacts != null) 
    {
        return Observable.of(this.contacts);
    } 
    else 
    {
        return this.http.get(url)
            .map(res => <Contact[]> res.json())
            .do(contacts => this.contacts = contacts)
            .catch(this.handleError);
    }
}