JavaScript - distance between points on the Earth in km

In this short article, we would like to show how to calculate the distance in km between two points on the Earth using JavaScript.

Hint: to know how to convert DMS format to decimal degrees check this article.

e.g. conversion:
from DMS format 51°53′N 176°39′W
to decimal degrees: {lat: 51.88333, lon: -176.65}.

Quick solution:

// ONLINE-RUNNER:browser;

const RADIAN = Math.PI / 180.0;
const RADIUS = 6371; // earth radius in km (https://dirask.com/posts/Constants-Earth-radius-in-km-p2YMAD)
const DIAMETER = 2 * RADIUS;

const toRadians = (degrees) => {
    return RADIAN * degrees;
};

// Calcultes distance from a to b points in km (a and b variables should be provided in radians).
//
const calculateDistance$1 = (a, b) => {
	const dLat = b.lat - a.lat;
	const dLon = b.lon - a.lon;
  	const aTmp = Math.sin(0.5 * dLat);
  	const bTmp = Math.sin(0.5 * dLon);
	const cTmp = aTmp * aTmp + bTmp * bTmp * Math.cos(a.lat) * Math.cos(b.lat);
	return DIAMETER * Math.atan2(Math.sqrt(cTmp), Math.sqrt(1.0 - cTmp));
};

// Calcultes distance from a to b points in km (a and b variables should be provided in degrees).
//
const calculateDistance$2 = (a, b) => {
  	const aTmp = {lat: toRadians(a.lat), lon: toRadians(a.lon)};
  	const bTmp = {lat: toRadians(b.lat), lon: toRadians(b.lon)};
  	return calculateDistance$1(aTmp, bTmp);
};


// Usage example:

const a = {lat: 51.5283080, lon:  -0.3817765}; // London City (United Kingdom)
const b = {lat: 40.6974034, lon: -74.1197612}; // New York City (USA)

const distance = calculateDistance$2(a, b);

console.log(distance);  // ~5561.352931973071 [km]

See also

1. Constants - Earth radius in km

2. JavaScript - convert longitude and latitude from degrees, minutes, and seconds (DMS) to decimal degrees (DD)