Tile Load Events

<!--
  示例：OpenLayers 瓦片加载事件
  要点：监听 tileloadstart / tileloadend / tileloaderror，统计并在页面上显示加载进度
  依赖：OpenLayers 10.3.1 · jsDelivr CDN
-->
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta name="robots" content="noindex,follow">
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>瓦片加载事件</title>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/ol@10.3.1/ol.css">
<style>
  html,body{height:100%;margin:0}
  body{display:flex;flex-direction:column;overflow:hidden;
       font:13px/1.6 -apple-system,"Segoe UI","PingFang SC",sans-serif}
  .bar{flex:0 0 auto;padding:8px 12px;background:#f6f7f9;border-bottom:1px solid #e3e6ea;
       display:flex;gap:10px;align-items:center;flex-wrap:wrap;font-size:12px;color:#58606e}
  .bar label{display:flex;gap:5px;align-items:center;cursor:pointer}
  .bar select,.bar input[type=range]{font-size:12px}
  .bar .val{font-family:ui-monospace,Consolas,monospace;color:#1f5fd0;min-width:44px}
  .bar .sep{width:1px;height:16px;background:#d8dce2}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
  .progress{width:180px;height:8px;background:#dde2e8;border-radius:4px;overflow:hidden}
  .progress > div{height:100%;width:0;background:#1f5fd0;transition:width .2s ease}
</style>
</head>
<body>
<div class="bar">
  <span>瓦片进度</span>
  <div class="progress"><div id="bar"></div></div>
  <span id="stat" class="val">0 / 0</span>
  <span class="sep"></span>
  <span id="err">错误 0</span>
</div>
<div id="map"></div>
<script src="https://cdn.jsdelivr.net/npm/ol@10.3.1/dist/ol.js"></script>
<script>
(function () {
  'use strict';

  if (typeof ol === 'undefined') {
    document.getElementById('map').textContent = 'OpenLayers 加载失败，请检查能否访问 cdn.jsdelivr.net';
    return;
  }


  var loading = 0;
  var loaded = 0;
  var errors = 0;
  var bar = document.getElementById('bar');
  var stat = document.getElementById('stat');
  var err = document.getElementById('err');

  function update() {
    var ratio = loading ? loaded / loading : 0;
    bar.style.width = (ratio * 100).toFixed(1) + '%';
    stat.textContent = loaded + ' / ' + loading;
    err.textContent = '错误 ' + errors;
  }

  var source = new ol.source.XYZ({url: 'https://server.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer/tile/{z}/{y}/{x}', attributions: 'Tiles © Esri'});

  source.on('tileloadstart', function () {
    ++loading;
    update();
  });
  source.on(['tileloadend', 'tileloaderror'], function (evt) {
    ++loaded;
    if (evt.type === 'tileloaderror') {
      ++errors;
    }
    update();
  });

  var map = new ol.Map({
    target: 'map',
    layers: [new ol.layer.Tile({source: source})],
    view: new ol.View({
      center: ol.proj.fromLonLat([116.391, 39.907]),
      zoom: 6
    })
  });

  map.on('loadstart', function () {
    bar.style.opacity = '1';
  });

  map.on('loadend', function () {
    window.setTimeout(function () {
      bar.style.opacity = '0.45';
    }, 300);
  });

  update();

})();
</script>
</body>
</html>