/**
 * 动态加载百度地图api函数
 * @param {String} ak  百度地图AK，必传
 */
 export default function loadBMap(ak) {
  return new Promise(function(resolve, reject) {
    if (typeof window.BMap !== 'undefined') {
      resolve(window.BMap);
      return true;
    }
    window.onBMapCallback = function() {
      resolve(window.BMap);
    };
    let script = document.createElement('script');
    script.type = 'text/javascript';
    script.src =
      'http://api.map.baidu.com/api?v=3.0&ak=' + ak + '&callback=onBMapCallback';
    script.onerror = reject;
    document.head.appendChild(script);
  });
}