Tooltip on Hover

Example of displaying feature information in tooltip by hovering.

In this example, a listener is registered on the map's pointermove to display the feature information in a tooltip when the pointer hovers over a feature.

main.js

import GeoJSON from 'ol/format/GeoJSON.js';
import Map from 'ol/Map.js';
import VectorLayer from 'ol/layer/Vector.js';
import VectorSource from 'ol/source/Vector.js';
import View from 'ol/View.js';

const vector = new VectorLayer({
  source: new VectorSource({
    url: 'https://openlayers.org/data/vector/ecoregions.json',
    format: new GeoJSON(),
  }),
  background: 'white',
  style: {
    'fill-color': ['string', ['get', 'COLOR'], '#eeeeee'],
  },
});

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

const info = document.getElementById('info');

let currentFeature;
const displayFeatureInfo = function (pixel, target) {
  const feature = target.closest('.ol-control')
    ? undefined
    : map.forEachFeatureAtPixel(pixel, function (feature) {
        return feature;
      });
  if (feature) {
    info.style.left = pixel[0] + 'px';
    info.style.top = pixel[1] + 'px';
    if (feature !== currentFeature) {
      info.style.visibility = 'visible';
      info.innerText = feature.get('ECO_NAME');
    }
  } else {
    info.style.visibility = 'hidden';
  }
  currentFeature = feature;
};

map.on('pointermove', function (evt) {
  if (evt.dragging) {
    info.style.visibility = 'hidden';
    currentFeature = undefined;
    return;
  }
  const pixel = map.getEventPixel(evt.originalEvent);
  displayFeatureInfo(pixel, evt.originalEvent.target);
});

map.on('click', function (evt) {
  displayFeatureInfo(evt.pixel, evt.originalEvent.target);
});

map.getTargetElement().addEventListener('pointerleave', function () {
  currentFeature = undefined;
  info.style.visibility = 'hidden';
});

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Tooltip on Hover</title>
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <style>
      .map {
        width: 100%;
        height: 400px;
      }
      #map {
        position: relative;
      }

      #info {
        position: absolute;
        display: inline-block;
        height: auto;
        width: auto;
        z-index: 100;
        background-color: #333;
        color: #fff;
        text-align: center;
        border-radius: 4px;
        padding: 5px;
        left: 50%;
        transform: translateX(3%);
        visibility: hidden;
        pointer-events: none;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map">
      <div id="info"></div>
    </div>

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

package.json

{
  "name": "tooltip-on-hover",
  "dependencies": {
    "ol": "9.1.0"
  },
  "devDependencies": {
    "vite": "^3.2.3"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}