"Find nearby X" features start here — with the same permission discipline as notifications.
The API
navigator.geolocation.getCurrentPosition(
(pos) => {
const { latitude, longitude, accuracy } = pos.coords;
showNearby(latitude, longitude);
},
(err) => {
// 1 = denied, 2 = unavailable, 3 = timeout
showManualCityPicker(); // ALWAYS have a fallback
},
{ enableHighAccuracy: false, timeout: 8000, maximumAge: 300000 }
);enableHighAccuracy: true= GPS: precise, slow, battery-hungry — only for maps/navigationmaximumAgeaccepts a cached fix — instant for "which city" purposes- HTTPS required; ask on user action ("Use my location" button), never on load
Distance between two points (Haversine)
function distanceKm(lat1, lon1, lat2, lon2) {
const R = 6371, toRad = (d) => (d * Math.PI) / 180;
const dLat = toRad(lat2 - lat1), dLon = toRad(lon2 - lon1);
const a = Math.sin(dLat/2)**2 +
Math.cos(toRad(lat1)) * Math.cos(toRad(lat2)) * Math.sin(dLon/2)**2;
return 2 * R * Math.asin(Math.sqrt(a));
}Project idea: "colleges near me" or a campus-navigation helper — geolocation + a static coordinates list + this formula. Free APIs for more: see 5 free APIs.