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

source 2

#####

Example of setting a layer source after construction.

Typically, the source for a layer is provided to the layer constructor. If you need to set a layer source after construction, this can be done with the `layer.setSource()` method.

The layer in the map above is constructed with no source. Use the links below to set/unset the layer source. A layer is not rendered until its source is set.

##### main.js

    import Map from 'ol/Map.js';
    import View from 'ol/View.js';
    import TileLayer from 'ol/layer/Tile.js';
    import OSM from 'ol/source/OSM.js';

    const source = new OSM();

    const layer = new TileLayer();

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

    document.getElementById('set-source').onclick = function () {
      layer.setSource(source);
    };

    document.getElementById('unset-source').onclick = function () {
      layer.setSource(null);
    };

##### index.html

    <!DOCTYPE html>
    <html lang="en">
      <head>
        <meta charset="UTF-8">
        <title>Lazy Source</title>
        <link rel="stylesheet" href="node_modules/ol/ol.css">
        <style>
          .map {
            width: 100%;
            height: 400px;
          }
           button.code {
             font-family: Monaco,Menlo,Consolas,"Courier New",monospace;
             font-size: 12px;
             padding: 5px;
             margin: 0 5px;
           }
        </style>
      </head>
      <body>
        <div id="map" class="map"></div>
        <button id="set-source" class="code">layer.setSource(source)</button>
        <button id="unset-source" class="code">layer.setSource(null)</button>

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

##### package.json

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