Min Zoom

<!--
  示例：最小缩放级别
  要点：View 的 minZoom 会夹住所有交互产生的级别，代码设置会被规整
  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>最小缩放级别</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;color:#16181d}
  .bar{flex:0 0 auto;padding:8px 12px;background:#f6f7f9;border-bottom:1px solid #e3e6ea;
       display:flex;gap:14px;align-items:center;font-size:12px;color:#58606e;flex-wrap:wrap}
  .bar button{padding:4px 10px;border:1px solid #d5dae2;background:#fff;border-radius:4px;cursor:pointer}
  .bar b{color:#16181d;font-weight:600}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <button id="out">缩小一级</button>
  <button id="in">放大一级</button>
  <span>minZoom <b id="min">5</b> / 当前 zoom <b id="z">—</b></span>
  <span id="msg">—</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 (!window.ol) {
    document.getElementById('map').textContent = 'OpenLayers 加载失败，请检查 cdn.jsdelivr.net 是否可访问';
    return;
  }

  var view = new ol.View({
    center: ol.proj.fromLonLat([116.391263, 39.907359]),
    zoom: 7,
    minZoom: 5,
    maxZoom: 12
  });

  var map = new ol.Map({
    target: 'map',
    layers: [new ol.layer.Tile({ source: new ol.source.XYZ({url: 'https://server.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer/tile/{z}/{y}/{x}', attributions: 'Tiles © Esri'}) })],
    view: view,
    controls: ol.control.defaults.defaults({ rotate: false })
  });

  function show() {
    document.getElementById('z').textContent = view.getZoom().toFixed(2);
    document.getElementById('min').textContent = view.getMinZoom();
  }

  /* 试图突破 minZoom 时，View 会自动夹回边界，不会抛错 */
  function zoomBy(delta) {
    var target = view.getZoom() + delta;
    view.animate({ zoom: target, duration: 250 });
    document.getElementById('msg').textContent =
      target < view.getMinZoom()
        ? '请求 ' + target.toFixed(1) + ' 级，被 minZoom 夹到 ' + view.getMinZoom()
        : target > view.getMaxZoom()
          ? '请求 ' + target.toFixed(1) + ' 级，被 maxZoom 夹到 ' + view.getMaxZoom()
          : '缩放到 ' + target.toFixed(1) + ' 级';
  }

  document.getElementById('out').addEventListener('click', function () { zoomBy(-2); });
  document.getElementById('in').addEventListener('click', function () { zoomBy(2); });

  map.on('moveend', show);
  show();

  /* 也可以运行时调整，调整后当前级别会被立即规整 */
  setTimeout(function () {
    view.setMinZoom(6);
    show();
    document.getElementById('msg').textContent = '运行中把 minZoom 提到 6，当前级别已按新边界检查';
  }, 100);
})();
</script>
</body>
</html>