This example uses OpenLayers v10.9.0. The latest is v.
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#### GeoJSON

geojson 11 vector 86 openstreetmap 22

#####

Example of GeoJSON features.

Example of GeoJSON features.

##### main.js

    import Feature from 'ol/Feature.js';
    import Map from 'ol/Map.js';
    import View from 'ol/View.js';
    import GeoJSON from 'ol/format/GeoJSON.js';
    import Circle from 'ol/geom/Circle.js';
    import TileLayer from 'ol/layer/Tile.js';
    import VectorLayer from 'ol/layer/Vector.js';
    import OSM from 'ol/source/OSM.js';
    import VectorSource from 'ol/source/Vector.js';
    import CircleStyle from 'ol/style/Circle.js';
    import Fill from 'ol/style/Fill.js';
    import Stroke from 'ol/style/Stroke.js';
    import Style from 'ol/style/Style.js';

    const image = new CircleStyle({
      radius: 5,
      fill: null,
      stroke: new Stroke({color: 'red', width: 1}),
    });

    const styles = {
      'Point': new Style({
        image: image,
      }),
      'LineString': new Style({
        stroke: new Stroke({
          color: 'green',
          width: 1,
        }),
      }),
      'MultiLineString': new Style({
        stroke: new Stroke({
          color: 'green',
          width: 1,
        }),
      }),
      'MultiPoint': new Style({
        image: image,
      }),
      'MultiPolygon': new Style({
        stroke: new Stroke({
          color: 'yellow',
          width: 1,
        }),
        fill: new Fill({
          color: 'rgba(255, 255, 0, 0.1)',
        }),
      }),
      'Polygon': new Style({
        stroke: new Stroke({
          color: 'blue',
          lineDash: [4],
          width: 3,
        }),
        fill: new Fill({
          color: 'rgba(0, 0, 255, 0.1)',
        }),
      }),
      'GeometryCollection': new Style({
        stroke: new Stroke({
          color: 'magenta',
          width: 2,
        }),
        fill: new Fill({
          color: 'magenta',
        }),
        image: new CircleStyle({
          radius: 10,
          fill: null,
          stroke: new Stroke({
            color: 'magenta',
          }),
        }),
      }),
      'Circle': new Style({
        stroke: new Stroke({
          color: 'red',
          width: 2,
        }),
        fill: new Fill({
          color: 'rgba(255,0,0,0.2)',
        }),
      }),
    };

    const styleFunction = function (feature) {
      return styles[feature.getGeometry().getType()];
    };

    const geojsonObject = {
      'type': 'FeatureCollection',
      'crs': {
        'type': 'name',
        'properties': {
          'name': 'EPSG:3857',
        },
      },
      'features': [
        {
          'type': 'Feature',
          'geometry': {
            'type': 'Point',
            'coordinates': [0, 0],
          },
        },
        {
          'type': 'Feature',
          'geometry': {
            'type': 'LineString',
            'coordinates': [
              [4e6, -2e6],
              [8e6, 2e6],
            ],
          },
        },
        {
          'type': 'Feature',
          'geometry': {
            'type': 'LineString',
            'coordinates': [
              [4e6, 2e6],
              [8e6, -2e6],
            ],
          },
        },
        {
          'type': 'Feature',
          'geometry': {
            'type': 'Polygon',
            'coordinates': [
              [
                [-5e6, -1e6],
                [-3e6, -1e6],
                [-4e6, 1e6],
                [-5e6, -1e6],
              ],
            ],
          },
        },
        {
          'type': 'Feature',
          'geometry': {
            'type': 'MultiLineString',
            'coordinates': [
              [
                [-1e6, -7.5e5],
                [-1e6, 7.5e5],
              ],
              [
                [1e6, -7.5e5],
                [1e6, 7.5e5],
              ],
              [
                [-7.5e5, -1e6],
                [7.5e5, -1e6],
              ],
              [
                [-7.5e5, 1e6],
                [7.5e5, 1e6],
              ],
            ],
          },
        },
        {
          'type': 'Feature',
          'geometry': {
            'type': 'MultiPolygon',
            'coordinates': [
              [
                [
                  [-5e6, 6e6],
                  [-3e6, 6e6],
                  [-3e6, 8e6],
                  [-5e6, 8e6],
                  [-5e6, 6e6],
                ],
              ],
              [
                [
                  [-2e6, 6e6],
                  [0, 6e6],
                  [0, 8e6],
                  [-2e6, 8e6],
                  [-2e6, 6e6],
                ],
              ],
              [
                [
                  [1e6, 6e6],
                  [3e6, 6e6],
                  [3e6, 8e6],
                  [1e6, 8e6],
                  [1e6, 6e6],
                ],
              ],
            ],
          },
        },
        {
          'type': 'Feature',
          'geometry': {
            'type': 'GeometryCollection',
            'geometries': [
              {
                'type': 'LineString',
                'coordinates': [
                  [-5e6, -5e6],
                  [0, -5e6],
                ],
              },
              {
                'type': 'Point',
                'coordinates': [4e6, -5e6],
              },
              {
                'type': 'Polygon',
                'coordinates': [
                  [
                    [1e6, -6e6],
                    [3e6, -6e6],
                    [2e6, -4e6],
                    [1e6, -6e6],
                  ],
                ],
              },
            ],
          },
        },
      ],
    };

    const vectorSource = new VectorSource({
      features: new GeoJSON().readFeatures(geojsonObject),
    });

    vectorSource.addFeature(new Feature(new Circle([5e6, 7e6], 1e6)));

    const vectorLayer = new VectorLayer({
      source: vectorSource,
      style: styleFunction,
    });

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

##### index.html

    <!DOCTYPE html>
    <html lang="en">
      <head>
        <meta charset="UTF-8">
        <title>GeoJSON</title>
        <link rel="stylesheet" href="node_modules/ol/ol.css">
        <style>
          .map {
            width: 100%;
            height: 400px;
          }
        </style>
      </head>
      <body>
        <div id="map" class="map"></div>

        <script type="module" src="main.js"></script>
      </body>
    </html>

##### package.json

    {
      "name": "geojson",
      "dependencies": {
        "ol": "10.9.0"
      },
      "devDependencies": {
        "vite": "^3.2.3"
      },
      "scripts": {
        "start": "vite",
        "build": "vite build"
      }
    }