Get the distance between two locations (latitude and longitude)

getDistance.js

getDistance = (origin, destination, unit = 'mi') => {
  // Convert degrees to radians
  const earthRadius = {
    'km': 6371,  // Earth radius in kilometers
    'mi': 3959 // Earth radius in miles
  };

  const originRad = origin.latitude * Math.PI / 180
  const destinationRad = destination.latitude * Math.PI / 180
  const dLat = destinationRad - originRad
  const dLon = (destination.longitude - origin.longitude) * Math.PI / 180

  const a = Math.sin(dLat / 2) * Math.sin(dLat / 2) +
            Math.cos(originRad) * Math.cos(destinationRad) *
            Math.sin(dLon / 2) * Math.sin(dLon / 2)

  const c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a))

  const distance = earthRadius[unit] * c

  return distance
}

// Birmingham New Street station
const origin = {
  latitude: 52.478150,
  longitude: -1.898960
}

// London Euston station
const destination = {
  latitude: 51.526450,
  longitude: -0.133740
}

// distance: 99.8090447964715 miles
console.log(getDistance(origin, destination))