Tile Load Events

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Tile Load Events

Example using tile load events.

Image tile sources fire events related to tile loading. You can listen for tileloadstart, tileloadend, and tileloaderror type events to monitor tile loading progress. This example registers listeners for these events and renders a tile loading progress bar at the bottom of the map.

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index.html<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Tile Load Events</title>
    <!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
    <script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
      .map {
        background: #E0ECED;
      }
      .wrapper {
        position: relative;
      }
      #progress {
        position: absolute;
        bottom: 0;
        left: 0;
        height: 2px;
        background: rgba(0, 60, 136, 0.4);
        width: 0;
        transition: width 250ms;
      }    </style>
  </head>
  <body>
    <div class="wrapper">
      <div id="map" class="map"></div>
      <div id="progress"></div>
    </div>
    <script src="index.js"></script>
  </body>
</html>

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index.jsimport 'ol/ol.css';
import Map from 'ol/Map';
import View from 'ol/View';
import TileLayer from 'ol/layer/Tile';
import TileJSON from 'ol/source/TileJSON';


/**
 * Renders a progress bar.
 * @param {HTMLElement} el The target element.
 * @constructor
 */
function Progress(el) {
  this.el = el;
  this.loading = 0;
  this.loaded = 0;
}


/**
 * Increment the count of loading tiles.
 */
Progress.prototype.addLoading = function() {
  if (this.loading === 0) {
    this.show();
  }
  ++this.loading;
  this.update();
};


/**
 * Increment the count of loaded tiles.
 */
Progress.prototype.addLoaded = function() {
  var this_ = this;
  setTimeout(function() {
    ++this_.loaded;
    this_.update();
  }, 100);
};


/**
 * Update the progress bar.
 */
Progress.prototype.update = function() {
  var width = (this.loaded / this.loading * 100).toFixed(1) + '%';
  this.el.style.width = width;
  if (this.loading === this.loaded) {
    this.loading = 0;
    this.loaded = 0;
    var this_ = this;
    setTimeout(function() {
      this_.hide();
    }, 500);
  }
};


/**
 * Show the progress bar.
 */
Progress.prototype.show = function() {
  this.el.style.visibility = 'visible';
};


/**
 * Hide the progress bar.
 */
Progress.prototype.hide = function() {
  if (this.loading === this.loaded) {
    this.el.style.visibility = 'hidden';
    this.el.style.width = 0;
  }
};

var progress = new Progress(document.getElementById('progress'));

var key = 'pk.eyJ1IjoidHNjaGF1YiIsImEiOiJjaW5zYW5lNHkxMTNmdWttM3JyOHZtMmNtIn0.CDIBD8H-G2Gf-cPkIuWtRg';
var source = new TileJSON({
  url: 'https://api.tiles.mapbox.com/v4/mapbox.world-bright.json?secure&access_token=' + key,
  crossOrigin: 'anonymous'
});

source.on('tileloadstart', function() {
  progress.addLoading();
});

source.on('tileloadend', function() {
  progress.addLoaded();
});
source.on('tileloaderror', function() {
  progress.addLoaded();
});

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

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package.json{
  "name": "tile-load-events",
  "dependencies": {
    "ol": "6.1.1"
  },
  "devDependencies": {
    "parcel": "1.11.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --experimental-scope-hoisting --public-url . index.html"
  }
}