too long

I want to build an app where a user posts some sort of text, the "blogpost" is accesible to anyone, but I only want people within a X KM radius to read it (display it on the feeds of users within that radius) What is the best way to do this? Thanks in advance.

Tried uploading the coordinates to a database, but not sure how to move on from there where the program checks for locations within the radius and then displays the blogpost

In Node.js, I would recommend using firestore with geofirex, so you can search within a certain radius, and thanks to firebase functions, you can even create real-time queries.

I made this web app that shows only points within a radius.

The main functions to store and read values are like this:

Reading

const DEFAULT_POINT = geo.point(32.520666, -117.021315);
const opinions = db.collection('opinions');

const opinionsSubscribe = () => {
  // Here we check opinions within 22km of radius
  // 'position' is the field where we store our geofirex point
  const query = reports.within(DEFAULT_POINT, 22, 'position');
  // This pipe just parse the data to geojson to make it easy to render directly on a map (tested with google and esri)
  const obs = query.pipe(toGeoJSON('position', true));
  obs.subscribe((geoj) => {
    console.log('reports changed');
    mainReportsData.geo = geoj;
    io.emit('reports', {
      metric: mainReportsData.geo,
    });
  });
};

opinionsSubscribe();

Writing

const storeOpinion = (uid, info, res) => {
  const {
    address,
    latitude,
    longitude,
    opinion,
  } = info;
  const lat = parseFloat(latitude);
  const lon = parseFloat(longitude);
  const timestamp = admin.firestore.FieldValue.serverTimestamp();
  // We use default firestore add function, so we need to extract the data from geofirex GeoPoint function
  const { data } = geo.point(lat, lon);
  // The attribute that stores entry location
  const position = {
    geopoint: new admin.firestore.GeoPoint(lat, lon),
    geohash: data.geohash,
  };
  opinions.add({
    address,
    timestamp,
    user: uid,
    position,
  })
    .then(() => {
      res.send({ data: 'success' });
    })
    .catch(() => {
      res.send({ data: 'error' });
    });
};

You can explore the code from this project, is almost the same code, feel free to ask any question.