geo.js

const EARTH_RADIUS = 6378137;

function toDeg(angle) {
    return angle * 180 / Math.PI;
}

function toRad(angle) {
    return angle * Math.PI / 180;
}

function solveDirectProblem3(lat, lng, azimuth, distance) {
    var δ = distance / EARTH_RADIUS;
    var θ = toRad(azimuth);
    var φ1 = toRad(lat);
    var λ1 = toRad(lng);

    var sinφ1 = Math.sin(φ1), 
        cosφ1 = Math.cos(φ1);
    var sinδ = Math.sin(δ), 
        cosδ = Math.cos(δ);
    var sinθ = Math.sin(θ), 
        cosθ = Math.cos(θ);

    var sinφ2 = sinφ1*cosδ + cosφ1*sinδ*cosθ;
    var φ2 = Math.asin(sinφ2);
    var y = sinθ * sinδ * cosφ1;
    var x = cosδ - sinφ1 * sinφ2;
    var λ2 = λ1 + Math.atan2(y, x);

    return [toDeg(φ2), toDeg(λ2)];
}