This example uses OpenLayers v10.9.0. The latest is v.
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#### Full Screen Control

full-screen 3 xyz 6 maptiler 26

#####

Example of a full screen control.

Click the control in the top right corner to go full screen. Click it again to exit full screen.

If there is no button on the map, your browser does not support the Full Screen API.

##### main.js

    import Map from 'ol/Map.js';
    import View from 'ol/View.js';
    import FullScreen from 'ol/control/FullScreen.js';
    import {defaults as defaultControls} from 'ol/control/defaults.js';
    import Layer from 'ol/layer/WebGLTile.js';
    import Source from 'ol/source/ImageTile.js';

    const view = new View({
      center: [-9101767, 2822912],
      zoom: 14,
    });

    const key = 'Get your own API key at https://www.maptiler.com/cloud/';
    const attributions =
      '<a href="https://www.maptiler.com/copyright/" target="_blank">&copy; MapTiler</a> ' +
      '<a href="https://www.openstreetmap.org/copyright" target="_blank">&copy; OpenStreetMap contributors</a>';

    const map = new Map({
      controls: defaultControls().extend([new FullScreen()]),
      layers: [
        new Layer({
          source: new Source({
            attributions: attributions,
            url:
              'https://api.maptiler.com/maps/satellite/{z}/{x}/{y}.jpg?key=' + key,
            tileSize: 512,
            maxZoom: 20,
          }),
        }),
      ],
      target: 'map',
      view: view,
    });

##### index.html

    <!DOCTYPE html>
    <html lang="en">
      <head>
        <meta charset="UTF-8">
        <title>Full Screen Control</title>
        <link rel="stylesheet" href="node_modules/ol/ol.css">
        <style>
          .map {
            width: 100%;
            height: 400px;
          }
          .map:-webkit-full-screen {
            height: 100%;
            margin: 0;
          }
          .map:fullscreen {
            height: 100%;
          }
          .map .ol-rotate {
            top: 3em;
          }
        </style>
      </head>
      <body>
        <div id="map" class="map"></div>

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

##### package.json

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