Put code in page.ts file

 getDistanceFromLatLonInKm(lat1,lon1,lat2,lon2) {
    var R = 6371; // Radius of the earth in km
    var dLat = this.deg2rad(lat2-lat1);  // deg2rad below
    var dLon = this.deg2rad(lon2-lon1); 
    var a =
        Math.sin(dLat/2) * Math.sin(dLat/2) +
        Math.cos(this.deg2rad(lat1)) * Math.cos(this.deg2rad(lat2)) * 
        Math.sin(dLon/2) * Math.sin(dLon/2);
        var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)); 
        var d = R * c; // Distance in km
        return d;
    }

     deg2rad(deg) {
      return deg * (Math.PI/180)
    }