title: rxjs obervable.interval(); throws not a function exception in browser
body: <p>The component.ts file is given below. Why it is throwing an error even after importing interval from rxjs/add/observable/interval.</p>
  
  <pre><code>import { Component, OnInit } from '@angular/core';
  import { Observable } from 'rxjs/Observable';
  import 'rxjs/add/observable/interval';
  @Component({
    selector: 'app-home',
    templateUrl: './home.component.html',
    styleUrls: ['./home.component.css']
  })
  export class HomeComponent implements OnInit {
  
    constructor() { }
    ngOnInit() {
        const myNumber = Observable.interval(1000);
        myNumber.subscribe(
          (number: number) =&gt; {
            console.log(number);
          }
        );
    }
  }
  </code></pre>
  
  <p><strong>Error Messages in the browser:</strong></p>
  
  <blockquote>
    <p>ERROR TypeError:
    rxjs_Observable__WEBPACK_IMPORTED_MODULE_2__.Observable.interval is
    not a function
        at HomeComponent.push../src/app/home/home.component.ts.HomeComponent.ngOnInit
    (home.component.ts:15)
        at checkAndUpdateDirectiveInline (core.js:20665)
        at checkAndUpdateNodeInline (core.js:21929)
        at checkAndUpdateNode (core.js:21891)
        at debugCheckAndUpdateNode (core.js:22525)
        at debugCheckDirectivesFn (core.js:22485)
        at Object.eval [as updateDirectives] (HomeComponent_Host.ngfactory.js? [sm]:1)
        at Object.debugUpdateDirectives [as updateDirectives] (core.js:22477)
        at checkAndUpdateView (core.js:21873)
        at callViewAction (core.js:22114) View_HomeComponent_Host_0 @ HomeComponent_Host.ngfactory.js? [sm]:1 proxyClass @ compiler.js:17945
    push../node_modules/@angular/core/fesm5/core.js.DebugContext_.logError
    @ core.js:22729
    push../node_modules/@angular/core/fesm5/core.js.ErrorHandler.handleError
    @ core.js:14645 (anonymous) @ core.js:16895
    push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invoke @
    zone.js:388 push../node_modules/zone.js/dist/zone.js.Zone.run @
    zone.js:138
    push../node_modules/@angular/core/fesm5/core.js.NgZone.runOutsideAngular
    @ core.js:16115
    push../node_modules/@angular/core/fesm5/core.js.ApplicationRef.tick @
    core.js:16895 (anonymous) @ core.js:16779
    push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invoke @
    zone.js:388 onInvoke @ core.js:16156
    push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invoke @
    zone.js:387 push../node_modules/zone.js/dist/zone.js.Zone.run @
    zone.js:138 push../node_modules/@angular/core/fesm5/core.js.NgZone.run
    @ core.js:16070 next @ core.js:16779 schedulerFn @ core.js:12609
    push../node_modules/rxjs/_esm5/internal/Subscriber.js.SafeSubscriber.<strong>tryOrUnsub @ Subscriber.js:196
    push../node_modules/rxjs/_esm5/internal/Subscriber.js.SafeSubscriber.next
    @ Subscriber.js:134
    push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber._next
    @ Subscriber.js:77
    push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber.next
    @ Subscriber.js:54
    push../node_modules/rxjs/_esm5/internal/Subject.js.Subject.next @
    Subject.js:47
    push../node_modules/@angular/core/fesm5/core.js.EventEmitter.emit @
    core.js:12593 checkStable @ core.js:16125 onHasTask @ core.js:16169
    push../node_modules/zone.js/dist/zone.js.ZoneDelegate.hasTask @
    zone.js:441
    push../node_modules/zone.js/dist/zone.js.ZoneDelegate._updateTaskCount
    @ zone.js:461
    push../node_modules/zone.js/dist/zone.js.Zone._updateTaskCount @
    zone.js:285 push../node_modules/zone.js/dist/zone.js.Zone.runTask @
    zone.js:205 drainMicroTaskQueue @ zone.js:595 Promise.then (async)
    scheduleMicroTask @ zone.js:578
    push../node_modules/zone.js/dist/zone.js.ZoneDelegate.scheduleTask @
    zone.js:410 push../node_modules/zone.js/dist/zone.js.Zone.scheduleTask
    @ zone.js:232
    push../node_modules/zone.js/dist/zone.js.Zone.scheduleMicroTask @
    zone.js:252 scheduleResolveOrReject @ zone.js:862
    ZoneAwarePromise.then @ zone.js:962
    push../node_modules/@angular/core/fesm5/core.js.PlatformRef.bootstrapModule
    @ core.js:16660 ./src/main.ts @ main.ts:11
    __webpack_require</strong> @ bootstrap:78 0 @ main.ts:12
    <strong>webpack_require</strong> @ bootstrap:78 checkDeferredModules @ bootstrap:45 webpackJsonpCallback @ bootstrap:32 (anonymous) @ main.js:1
    HomeComponent_Host.ngfactory.js? [sm]:1 ERROR CONTEXT
    DebugContext_ {view: {…}, nodeIndex: 0, nodeDef: {…}, elDef: {…},
    elView: {…}} View_HomeComponent_Host_0 @
    HomeComponent_Host.ngfactory.js? [sm]:1 proxyClass @ compiler.js:17945
    push../node_modules/@angular/core/fesm5/core.js.DebugContext_.logError
    @ core.js:22729
    push../node_modules/@angular/core/fesm5/core.js.ErrorHandler.handleError
    @ core.js:14650 (anonymous) @ core.js:16895
    push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invoke @
    zone.js:388 push../node_modules/zone.js/dist/zone.js.Zone.run @
    zone.js:138
    push../node_modules/@angular/core/fesm5/core.js.NgZone.runOutsideAngular
    @ core.js:16115
    push../node_modules/@angular/core/fesm5/core.js.ApplicationRef.tick @
    core.js:16895 (anonymous) @ core.js:16779
    push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invoke @
    zone.js:388 onInvoke @ core.js:16156
    push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invoke @
    zone.js:387 push../node_modules/zone.js/dist/zone.js.Zone.run @
    zone.js:138 push../node_modules/@angular/core/fesm5/core.js.NgZone.run
    @ core.js:16070 next @ core.js:16779 schedulerFn @ core.js:12609
    push../node_modules/rxjs/_esm5/internal/Subscriber.js.SafeSubscriber.<strong>tryOrUnsub @ Subscriber.js:196
    push../node_modules/rxjs/_esm5/internal/Subscriber.js.SafeSubscriber.next
    @ Subscriber.js:134
    push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber._next
    @ Subscriber.js:77
    push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber.next
    @ Subscriber.js:54
    push../node_modules/rxjs/_esm5/internal/Subject.js.Subject.next @
    Subject.js:47
    push../node_modules/@angular/core/fesm5/core.js.EventEmitter.emit @
    core.js:12593 checkStable @ core.js:16125 onHasTask @ core.js:16169
    push../node_modules/zone.js/dist/zone.js.ZoneDelegate.hasTask @
    zone.js:441
    push../node_modules/zone.js/dist/zone.js.ZoneDelegate._updateTaskCount
    @ zone.js:461
    push../node_modules/zone.js/dist/zone.js.Zone._updateTaskCount @
    zone.js:285 push../node_modules/zone.js/dist/zone.js.Zone.runTask @
    zone.js:205 drainMicroTaskQueue @ zone.js:595 Promise.then (async)
    scheduleMicroTask @ zone.js:578
    push../node_modules/zone.js/dist/zone.js.ZoneDelegate.scheduleTask @
    zone.js:410 push../node_modules/zone.js/dist/zone.js.Zone.scheduleTask
    @ zone.js:232
    push../node_modules/zone.js/dist/zone.js.Zone.scheduleMicroTask @
    zone.js:252 scheduleResolveOrReject @ zone.js:862
    ZoneAwarePromise.then @ zone.js:962
    push../node_modules/@angular/core/fesm5/core.js.PlatformRef.bootstrapModule
    @ core.js:16660 ./src/main.ts @ main.ts:11
    __webpack_require</strong> @ bootstrap:78 0 @ main.ts:12
    <strong>webpack_require</strong> @ bootstrap:78 checkDeferredModules @ bootstrap:45 webpackJsonpCallback @ bootstrap:32 (anonymous) @ main.js:1</p>
  </blockquote>