geojson-vt integration

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index.html<!DOCTYPE html>
<html lang="en">
  <head>
    <title>geojson-vt integration</title>
    <!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
    <script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
    <script src="https://mapbox.github.io/geojson-vt/geojson-vt-dev.js"></script>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <script src="index.js"></script>
  </body>
</html>

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index.jsimport 'ol/ol.css';
import Map from 'ol/Map';
import View from 'ol/View';
import GeoJSON from 'ol/format/GeoJSON';
import OSM from 'ol/source/OSM';
import VectorTileSource from 'ol/source/VectorTile';
import {Tile as TileLayer, VectorTile as VectorTileLayer} from 'ol/layer';
import Projection from 'ol/proj/Projection';

// Converts geojson-vt data to GeoJSON
var replacer = function(key, value) {
  if (value.geometry) {
    var type;
    var rawType = value.type;
    var geometry = value.geometry;

    if (rawType === 1) {
      type = 'MultiPoint';
      if (geometry.length == 1) {
        type = 'Point';
        geometry = geometry[0];
      }
    } else if (rawType === 2) {
      type = 'MultiLineString';
      if (geometry.length == 1) {
        type = 'LineString';
        geometry = geometry[0];
      }
    } else if (rawType === 3) {
      type = 'Polygon';
      if (geometry.length > 1) {
        type = 'MultiPolygon';
        geometry = [geometry];
      }
    }

    return {
      'type': 'Feature',
      'geometry': {
        'type': type,
        'coordinates': geometry
      },
      'properties': value.tags
    };
  } else {
    return value;
  }
};

var map = new Map({
  layers: [
    new TileLayer({
      source: new OSM()
    })
  ],
  target: 'map',
  view: new View({
    center: [0, 0],
    zoom: 2
  })
});

var url = 'data/geojson/countries.geojson';
fetch(url).then(function(response) {
  return response.json();
}).then(function(json) {
  var tileIndex = geojsonvt(json, {
    extent: 4096,
    debug: 1
  });
  var vectorSource = new VectorTileSource({
    format: new GeoJSON({
      // Data returned from geojson-vt is in tile pixel units
      dataProjection: new Projection({
        code: 'TILE_PIXELS',
        units: 'tile-pixels',
        extent: [0, 0, 4096, 4096]
      })
    }),
    tileUrlFunction: function(tileCoord) {
      var data = tileIndex.getTile(tileCoord[0], tileCoord[1], tileCoord[2]);
      var geojson = JSON.stringify({
        type: 'FeatureCollection',
        features: data ? data.features : []
      }, replacer);
      return 'data:application/json;charset=UTF-8,' + geojson;
    }
  });
  var vectorLayer = new VectorTileLayer({
    source: vectorSource
  });
  map.addLayer(vectorLayer);
});

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package.json{
  "name": "geojson-vt",
  "dependencies": {
    "ol": "6.1.1"
  },
  "devDependencies": {
    "parcel": "1.11.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --experimental-scope-hoisting --public-url . index.html"
  }
}