watchPosition

page.ts

import { Geolocation } from '@ionic-native/geolocation';

...

constructor(private geolocation: Geolocation) {}

...

let watch = this.geolocation.watchPosition();
watch.subscribe((data) => {
 // data can be a set of coordinates, or an error (if an error occurred).
 // data.coords.latitude
 // data.coords.longitude
});