ERROR TypeError: firebase.messaging is not a function

I'm getting error, ERROR TypeError: firebase.messaging is not a function Whats wrong with it ?

import { Injectable } from '@angular/core';
import { AngularFireDatabase } from 'angularfire2/database';
import { AngularFireAuth} from 'angularfire2/auth';
import * as firebase from 'firebase/app';

import 'rxjs/add/operator/take';
import { BehaviorSubject} from 'rxjs/BehaviorSubject';

@Injectable()
export class MessagingService {

messaging = firebase.messaging();
currentMessage = new BehaviorSubject(null);

constructor(private db: AngularFireDatabase, private afAuth: 
AngularFireAuth) {
}

private updateToken(token) {
  this.afAuth.authState.take(1).subscribe(user => {
    if (!user) { return; }

    const data = { [user.uid]: token };
    this.db.object('fcmTokens/').update(data);
  });
}

getPermission() {
    this.messaging.requestPermission()
        .then(() => {
            console.log('Notification permission granted.');
            return this.messaging.getToken();
        })
        .then(token => {
            console.log(token);
            this.updateToken(token);
        })
        .catch((err) => {
            console.log('Unable to get permission to notify.', err);
        });
} 

receiveMessage() {
    this.messaging.onMessage((payload) => {
        console.log('Message received. ', payload);
        this.currentMessage.next(payload);
    });
  }
}

ERROR TypeError: firebase.messaging is not a function I'm having big probleems with that error, I don't have any idea how to fix that, please help me repair that code. I've done everything like an example, but it doesn't work. thank you so much for your answers.