JavaScript - distance between points on the Earth in km

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]