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

draw 17 vector 86 arrow 2

#####

Example of drawing arrows for each line string segment.

Example of drawing arrows for each line string segment.

##### main.js

    import Map from 'ol/Map.js';
    import View from 'ol/View.js';
    import Point from 'ol/geom/Point.js';
    import Draw from 'ol/interaction/Draw.js';
    import TileLayer from 'ol/layer/Tile.js';
    import VectorLayer from 'ol/layer/Vector.js';
    import {get} from 'ol/proj.js';
    import OSM from 'ol/source/OSM.js';
    import VectorSource from 'ol/source/Vector.js';
    import Icon from 'ol/style/Icon.js';
    import Stroke from 'ol/style/Stroke.js';
    import Style from 'ol/style/Style.js';

    const raster = new TileLayer({
      source: new OSM(),
    });

    const source = new VectorSource();

    const styleFunction = function (feature) {
      const geometry = feature.getGeometry();
      const styles = [
        // linestring
        new Style({
          stroke: new Stroke({
            color: '#ffcc33',
            width: 2,
          }),
        }),
      ];

      geometry.forEachSegment(function (start, end) {
        const dx = end[0] - start[0];
        const dy = end[1] - start[1];
        const rotation = Math.atan2(dy, dx);
        // arrows
        styles.push(
          new Style({
            geometry: new Point(end),
            image: new Icon({
              src: 'data/arrow.png',
              anchor: [0.75, 0.5],
              rotateWithView: true,
              rotation: -rotation,
            }),
          }),
        );
      });

      return styles;
    };
    const vector = new VectorLayer({
      source: source,
      style: styleFunction,
    });

    // Limit multi-world panning to one world east and west of the real world.
    // Geometry coordinates have to be within that range.
    const extent = get('EPSG:3857').getExtent().slice();
    extent[0] += extent[0];
    extent[2] += extent[2];

    const map = new Map({
      layers: [raster, vector],
      target: 'map',
      view: new View({
        center: [-11000000, 4600000],
        zoom: 4,
        extent,
      }),
    });

    map.addInteraction(
      new Draw({
        source: source,
        type: 'LineString',
      }),
    );

##### index.html

    <!DOCTYPE html>
    <html lang="en">
      <head>
        <meta charset="UTF-8">
        <title>LineString Arrows</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": "line-arrows",
      "dependencies": {
        "ol": "10.9.0"
      },
      "devDependencies": {
        "vite": "^3.2.3"
      },
      "scripts": {
        "start": "vite",
        "build": "vite build"
      }
    }