This might be helpful in Angular 6 for more info refer this Document

1. rxjs: Creation methods, types, schedulers and utilities

import { Observable, Subject, asapScheduler, pipe, of, from, interval, merge, fromEvent } from 'rxjs';

2. rxjs/operators: All pipeable operators:

import { map, filter, scan } from 'rxjs/operators';

3. rxjs/webSocket: The web socket subject implementation

import { webSocket } from 'rxjs/webSocket';

4. rxjs/ajax: The Rx ajax implementation

import { ajax } from 'rxjs/ajax';

5. rxjs/testing: The testing utilities

import { TestScheduler } from 'rxjs/testing';