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

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);
};