Calculate distance between Latitude/Longitude points. This uses the 'haversine' formula to calculate the great-circle distance between two points.

distance_calculator.ts

// Calculate distance between Latitude/Longitude points
// This uses the ‘haversine’ formula to calculate the great-circle distance between two points.

// Sources:
//      http://www.movable-type.co.uk/scripts/latlong.html
//      https://stackoverflow.com/questions/27928/calculate-distance-between-two-latitude-longitude-points-haversine-formula
//      Distance in km

function deg2rad(deg): number {
  return deg * (Math.PI/180);
}

function getDistanceInKm( lat1: number, lon1: number, lat2: number, lon2: number ) : number {
        
  let R: number = 6371; // Earth's radius (km)

  let dLat: number = deg2rad(lat2 - lat1);
  let dLon: number = deg2rad(lon2 - lon1); 

  let a: number = Math.sin(dLat/2) * Math.sin(dLat/2) + Math.cos(deg2rad(lat1)) * Math.cos(deg2rad(lat2)) * Math.sin(dLon / 2) * Math.sin(dLon / 2);
     
  let c: number = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)); 
  let d: number = R * c; // Distance in km
  return d;
}

// Testing: distance between Mexico city and Queretaro
document.body.innerHTML = String(getDistanceInKm(19.4326077, -99.13320799999997, 20.5888184, -100.38988760000001));