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

vector 86

#####

Synthetic points example.

##### main.js

    import Feature from 'ol/Feature.js';
    import Map from 'ol/Map.js';
    import View from 'ol/View.js';
    import LineString from 'ol/geom/LineString.js';
    import Point from 'ol/geom/Point.js';
    import VectorLayer from 'ol/layer/Vector.js';
    import {getVectorContext} from 'ol/render.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 count = 20000;
    const features = new Array(count);
    const e = 18000000;
    for (let i = 0; i < count; ++i) {
      features[i] = new Feature({
        'geometry': new Point([
          2 * e * Math.random() - e,
          2 * e * Math.random() - e,
        ]),
        'i': i,
        'size': i % 2 ? 10 : 20,
      });
    }

    const styles = {
      '10': new Style({
        image: new CircleStyle({
          radius: 5,
          fill: new Fill({color: '#666666'}),
          stroke: new Stroke({color: '#bada55', width: 1}),
        }),
      }),
      '20': new Style({
        image: new CircleStyle({
          radius: 10,
          fill: new Fill({color: '#666666'}),
          stroke: new Stroke({color: '#bada55', width: 1}),
        }),
      }),
    };

    const vectorSource = new VectorSource({
      features: features,
      wrapX: false,
    });
    const vector = new VectorLayer({
      source: vectorSource,
      style: function (feature) {
        return styles[feature.get('size')];
      },
    });

    const map = new Map({
      layers: [vector],
      target: document.getElementById('map'),
      view: new View({
        center: [0, 0],
        zoom: 2,
      }),
    });

    let point = null;
    let line = null;
    const displaySnap = function (coordinate) {
      const closestFeature = vectorSource.getClosestFeatureToCoordinate(coordinate);
      if (closestFeature === null) {
        point = null;
        line = null;
      } else {
        const geometry = closestFeature.getGeometry();
        const closestPoint = geometry.getClosestPoint(coordinate);
        if (point === null) {
          point = new Point(closestPoint);
        } else {
          point.setCoordinates(closestPoint);
        }
        if (line === null) {
          line = new LineString([coordinate, closestPoint]);
        } else {
          line.setCoordinates([coordinate, closestPoint]);
        }
      }
      map.render();
    };

    map.on('pointermove', function (evt) {
      if (evt.dragging) {
        return;
      }
      const coordinate = map.getEventCoordinate(evt.originalEvent);
      displaySnap(coordinate);
    });

    map.on('click', function (evt) {
      displaySnap(evt.coordinate);
    });

    const stroke = new Stroke({
      color: 'rgba(255,255,0,0.9)',
      width: 3,
    });
    const style = new Style({
      stroke: stroke,
      image: new CircleStyle({
        radius: 10,
        stroke: stroke,
      }),
    });

    vector.on('postrender', function (evt) {
      const vectorContext = getVectorContext(evt);
      vectorContext.setStyle(style);
      if (point !== null) {
        vectorContext.drawGeometry(point);
      }
      if (line !== null) {
        vectorContext.drawGeometry(line);
      }
    });

    map.on('pointermove', function (evt) {
      if (evt.dragging) {
        return;
      }
      const hit = map.hasFeatureAtPixel(evt.pixel);
      map.getTargetElement().style.cursor = hit ? 'pointer' : '';
    });

##### index.html

    <!DOCTYPE html>
    <html lang="en">
      <head>
        <meta charset="UTF-8">
        <title>Synthetic Points</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": "synthetic-points",
      "dependencies": {
        "ol": "10.9.0"
      },
      "devDependencies": {
        "vite": "^3.2.3"
      },
      "scripts": {
        "start": "vite",
        "build": "vite build"
      }
    }