App development classes for teens in Canada

// Our spray pad finder logic (Modern Age Coders, written for this page). Runs in Node or inside a React Native app.
const fs = require("fs");

function distanceKm(lat1, lon1, lat2, lon2) {
  const R = 6371;                                   // mean Earth radius in km
  const rad = (d) => (d * Math.PI) / 180;
  const dLat = rad(lat2 - lat1);
  const dLon = rad(lon2 - lon1);
  const h = Math.sin(dLat / 2) ** 2 +
            Math.cos(rad(lat1)) * Math.cos(rad(lat2)) * Math.sin(dLon / 2) ** 2;
  return 2 * R * Math.asin(Math.sqrt(h));           // the haversine formula
}

function loadPads(path) {
  const [header, ...lines] = fs.readFileSync(path, "utf8").replace(/^\uFEFF/, "").trim().split(/\r?\n/);
  const cols = header.split(",");
  return lines.map((line) => {
    const f = line.split(",");                      // safe here: this file has no quoted fields
    return { name: f[cols.indexOf("NAME")], lat: Number(f[cols.indexOf("Y")]), lon: Number(f[cols.indexOf("X")]) };
  });
}

function nearest(pads, lat, lon, n) {
  return pads
    .map((p) => ({ ...p, km: distanceKm(lat, lon, p.lat, p.lon) }))
    .sort((a, b) => a.km - b.km)
    .slice(0, n);
}

const pads = loadPads("hamilton-spray-pads.csv");
const here = { lat: 43.2557, lon: -79.8711 };       // our example point, downtown Hamilton
console.log(pads.length, "spray pads loaded");
for (const p of nearest(pads, here.lat, here.lon, 4)) {
  console.log(p.name.padEnd(14), p.km.toFixed(2), "km");
}

68 spray pads loaded
Durand Park    0.70 km
Beasley Park   0.74 km
McLaren Park   0.80 km
Central Park   0.94 km

The same functions drop into a React Native screen unchanged; only loadPads changes, because an app bundles or downloads the data instead of reading a file.