js 异步加载百度地图

  async loadBMap() {
    if (!window.Bmap) {
      let urls = [
        'http://api.map.baidu.com/api?v=3.0&ak=key&callback=onBMapCallback',
        'http://api.map.baidu.com/library/LuShu/1.2/src/LuShu_min.js',
        'http://api.map.baidu.com/library/AreaRestriction/1.2/src/AreaRestriction_min.js'
      ];

      for (let i = 0; i < urls.length; i++) {
        await new Promise((res, rej) => {
          let script = document.createElement('script');
          script.src = urls[i];
          if (i === 1) {
            window.onBMapCallback = () => {
              res();
            };
          } else {
            script.onload = () => {
              res();
            };
          }
          script.onerror = rej;
          document.head.appendChild(script);
        });
      }
    }
  }