measure-coordinate-distance.js

function measure(lat1, lon1, lat2, lon2){  // generally used geo measurement function
  const { PI, cos, sin, sqrt, atan2 } = Math // math fns
  const R = 6378.137 // Radius of earth in KM
  // PI is equivilant to 180 degrees, so divide PI by 180 
  // and you get how many radians constitute a single degree
  const radsInSingleDegree = (PI / 180)
  // Get the amount of radians between the two coordinates 
  const [dLat, dLon] = [
    (lat2 * radsInSingleDegree) - (lat1 * radsInSingleDegree),
    (lon2 * radsInSingleDegree) - (lon1 * radsInSingleDegree),
  ]
  const a = sin(dLat / 2) * sin(dLat / 2) + cos(lat1 * radsInSingleDegree) * cos(lat2 * radsInSingleDegree) * sin(dLon / 2) * sin(dLon / 2)
  var c = 2 * atan2(sqrt(a), sqrt(1-a))
  const km = (R * c) // kilometers
  return km * 1000; // meters
}