Transform a JSON array using streams

transform_json_streaming.js

const fs = require('fs')
const transfuse = require('transfuse')
const stationsStream = fs.createReadStream('./stations.json')
const geoJSONStream = fs.createWriteStream('./stations.geojson', { autoClose: false })

const stationTransformer = transfuse((doc, map) => {
  if (doc.lng > 180.0 || doc.lng < -180.0 ||
      doc.lat > 90.0 || doc.lat < -90.0) {

    console.log('malformed location', doc.naam)
    return map()
  }

  map({
    type: 'Feature',
    properties: {
      name: doc.naam
    },
    geometry: {
      type: 'Point',
      coordinates: [
        doc.lng,
        doc.lat
      ]
    }
  });
});

// Header
geoJSONStream.write('{"type": "FeatureCollection", "features": ', 'utf8')

// Footer
// (nothing more to read from the stationsStream, end the writer)
stationTransformer.on('end', () => {
  geoJSONStream.write('}', 'utf8')
  geoJSONStream.end()
})

stationsStream
  .pipe(stationTransformer)
  .pipe(geoJSONStream, { end: false })