Compute distance in km between two coordinates using the haversine formula

haversine.js

const haversine = (pos1, pos2) => {    
    // https://stackoverflow.com/questions/639695/how-to-convert-latitude-or-longitude-to-meters
    const R = 6378.137; // Radius of Earth
    const dLat = pos2.lat * Math.PI / 180 - pos1.lat * Math.PI / 180;
    const dLon = pos2.lng * Math.PI / 180 - pos1.lng * Math.PI / 180;
    const a = Math.sin(dLat/2) * Math.sin(dLat/2) +
        Math.cos(pos1.lat * Math.PI / 180) * Math.cos(pos2.lat * Math.PI / 180) *
        Math.sin(dLon/2) * Math.sin(dLon/2);
    return (R * 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)));
};