Edit

Uses an overlay to create a popup.

Click on the map to get a popup. The popup is composed of a few basic elements: a container, a close button, and a place for the content. To anchor the popup to the map, an ol/Overlay is created with the popup container. A listener is registered for the map's click event to display the popup, and another listener is set as the click handler for the close button to hide the popup.

main.js
import Map from 'ol/Map.js';
import Overlay from 'ol/Overlay.js';
import TileLayer from 'ol/layer/Tile.js';
import View from 'ol/View.js';
import XYZ from 'ol/source/XYZ.js';
import {toLonLat} from 'ol/proj.js';
import {toStringHDMS} from 'ol/coordinate.js';

/**
 * Elements that make up the popup.
 */
const container = document.getElementById('popup');
const content = document.getElementById('popup-content');
const closer = document.getElementById('popup-closer');

/**
 * Create an overlay to anchor the popup to the map.
 */
const overlay = new Overlay({
  element: container,
  autoPan: {
    animation: {
      duration: 250,
    },
  },
});

/**
 * Add a click handler to hide the popup.
 * @return {boolean} Don't follow the href.
 */
closer.onclick = function () {
  overlay.setPosition(undefined);
  closer.blur();
  return false;
};

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>';

/**
 * Create the map.
 */
const map = new Map({
  layers: [
    new TileLayer({
      source: new XYZ({
        attributions: attributions,
        url: 'https://api.maptiler.com/maps/streets/{z}/{x}/{y}.png?key=' + key,
        tileSize: 512,
      }),
    }),
  ],
  overlays: [overlay],
  target: 'map',
  view: new View({
    center: [0, 0],
    zoom: 2,
  }),
});

/**
 * Add a click handler to the map to render the popup.
 */
map.on('singleclick', function (evt) {
  const coordinate = evt.coordinate;
  const hdms = toStringHDMS(toLonLat(coordinate));

  content.innerHTML = '<p>You clicked here:</p><code>' + hdms + '</code>';
  overlay.setPosition(coordinate);
});
index.html
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Popup</title>
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <style>
      .map {
        width: 100%;
        height: 400px;
      }
      .ol-popup {
        position: absolute;
        background-color: white;
        box-shadow: 0 1px 4px rgba(0,0,0,0.2);
        padding: 15px;
        border-radius: 10px;
        border: 1px solid #cccccc;
        bottom: 12px;
        left: -50px;
        min-width: 280px;
      }
      .ol-popup:after, .ol-popup:before {
        top: 100%;
        border: solid transparent;
        content: " ";
        height: 0;
        width: 0;
        position: absolute;
        pointer-events: none;
      }
      .ol-popup:after {
        border-top-color: white;
        border-width: 10px;
        left: 48px;
        margin-left: -10px;
      }
      .ol-popup:before {
        border-top-color: #cccccc;
        border-width: 11px;
        left: 48px;
        margin-left: -11px;
      }
      .ol-popup-closer {
        text-decoration: none;
        position: absolute;
        top: 2px;
        right: 8px;
      }
      .ol-popup-closer:after {
        content: "✖";
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <div id="popup" class="ol-popup">
      <a href="#" id="popup-closer" class="ol-popup-closer"></a>
      <div id="popup-content"></div>
    </div>

    <script type="module" src="main.js"></script>
  </body>
</html>
package.json
{
  "name": "popup",
  "dependencies": {
    "ol": "9.0.0"
  },
  "devDependencies": {
    "vite": "^3.2.3"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}