Tile Error

<!--
  示例：瓦片错误处理
  要点：监听 tileloaderror 记录瓦片编号，连续失败后自动切回可用数据源
  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>瓦片错误处理</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;font-size:12px;color:#58606e;flex-wrap:wrap}
  .bar button{padding:4px 10px;border:1px solid #cfd4dc;border-radius:4px;
              background:#fff;cursor:pointer;font-size:12px}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
  #log{font-family:ui-monospace,Consolas,monospace;color:#c2410c}
</style>
</head>
<body>
<div class="bar">
  <button id="break">模拟故障</button>
  <button id="restore">恢复底图</button>
  <button id="clear">清空记录</button>
  <span id="stat">失败 0 次</span>
  <span id="log">—</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').innerHTML =
      '<div style="padding:20px;color:#b42318">OpenLayers 加载失败，请检查能否访问 cdn.jsdelivr.net</div>';
    return;
  }

  var base = new ol.layer.Tile();

  var stat = document.getElementById('stat');
  var log = document.getElementById('log');

  var errors = [];
  var total = 0;
  var broken = false;

  function report() {
    stat.textContent = '失败 ' + total + ' 次';
    log.textContent = errors.length ? errors.join('  ') : '—';
  }

  /* 换源后必须重新绑定事件 */
  function useSource(source) {
    base.setSource(source);
    source.on('tileloaderror', function (evt) {
      var tile = evt.tile;
      var coord = tile && tile.getTileCoord ? tile.getTileCoord() : ['?'];
      total++;
      errors.unshift(coord.join('/'));
      errors = errors.slice(0, 8);
      report();

      /* 连续失败到阈值就自动降级 */
      if (broken && total >= 5) {
        restore(true);
      }
    });
  }

  function restore(auto) {
    broken = false;
    errors = [];
    total = 0;
    useSource(new ol.source.XYZ({url: 'https://server.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer/tile/{z}/{y}/{x}', attributions: 'Tiles © Esri'}));
    report();
    log.textContent = auto ? '已自动降级到 OSM 底图' : '已恢复 OSM 底图';
  }

  var view = new ol.View({
    center: ol.proj.fromLonLat([116.3974, 39.9093]),
    zoom: 13
  });

  new ol.Map({
    target: 'map',
    layers: [base],
    view: view,
    controls: ol.control.defaults.defaults({ attribution: false })
  });

  restore(false);

  document.getElementById('break').addEventListener('click', function () {
    broken = true;
    errors = [];
    total = 0;
    useSource(new ol.source.XYZ({
      url: 'https://tile.invalid/{z}/{x}/{y}.png',
      crossOrigin: null
    }));
    report();
    log.textContent = '正在请求无效地址…';
  });

  document.getElementById('restore').addEventListener('click', function () {
    restore(false);
  });

  document.getElementById('clear').addEventListener('click', function () {
    errors = [];
    total = 0;
    report();
  });
})();
</script>
</body>
</html>