Update google marker with watchposition in ionic - ionic-framework

Question

I am creating a map to track user position, i am using #geolocation plugin and showing map using:
<script src="https://maps.googleapis.com/maps/api/js?key=API_KEYscript>
Currently marker is being displayed and on watchposition marker is placing multiple times and isn’t removing last placed marker.
import { Component, ViewChild, ElementRef } from '#angular/core';
import { Geolocation, GeolocationOptions, Geoposition, PositionError } from '#ionic-native/geolocation';
declare var google;
#Component({
selector: 'app-tab1',
templateUrl: 'tab1.page.html',
styleUrls: ['tab1.page.scss']
})
export class Tab1Page {
geolocation = Geolocation;
options: GeolocationOptions;
currentPos: Geoposition;
#ViewChild('map', { static: false }) mapElement: ElementRef;
map: any;
constructor() { }
ionViewDidEnter() {
this.getUserPosition();
}
getUserPosition() {
this.options = {
enableHighAccuracy: false
};
//get location
this.geolocation.getCurrentPosition(this.options).then((pos: Geoposition) => {
this.currentPos = pos;
console.log(pos);
//add map
let latLng = new google.maps.LatLng(pos.coords.latitude, pos.coords.longitude);
let mapOptions = {
center: latLng,
zoom: 18,
mapTypeId: google.maps.MapTypeId.ROADMAP
}
this.map = new google.maps.Map(this.mapElement.nativeElement, mapOptions);
this.addMarker(latLng);
}, (err: PositionError) => {
console.log("error : " + err.message);
})
let subscription = this.geolocation.watchPosition().subscribe(position =>{
let userPosition = new google.maps.LatLng(position.coords.latitude, position.coords.longitude);
this.addMarker(userPosition);
})
}
addMarker(position) {
let marker = new google.maps.Marker({
map: this.map,
animation: google.maps.Animation.DROP,
position: position
});
let content = "<p>This is your current position !</p>";
let infoWindow = new google.maps.InfoWindow({
content: content
});
google.maps.event.addListener(marker, 'click', () => {
infoWindow.open(this.map, marker);
});
}
}
I want to remove last marker before placing another one.
Thank you.