单例模式的目标是确保一个类只有一个实例，并提供一个全局访问点来访问该实例。
advMaster.js

export const advManager = new (class {
  constructor() {
    this.sourceList = [];
    this.pendingPromise = null;
  }

  initialize(sources) {
    this.sourceList = sources;
  }

  requestAd(id) {
    return new Promise((resolve, reject) => {
      if (this.pendingPromise) {
        this.pendingPromise.then((result) => resolve(this.findAd(result, id)));
      } else {
        this.pendingPromise = advMasterApi.getBannerInfos(
          this.sourceList,
          config.env === 'development' ? 'staging' : config.env,
          { systemCode: getSystemCode() },
        )
          .then((adxData = {}) => {
            const { adm = [] } = adxData;
            if (adm && adm.length > 0) {
              resolve(this.findAd(adm, id));
              return adm;
            }
            reject(new Error('No advertising data available'));
            return [];
          })
          .catch(reject);
      }
    });
  }

  findAd(adList, id) {
    return (adList || []).find((ad) => ad.impid === id);
  }
})();

index.vue

const adResources = ['123', '456'];
advManager.initialize(adResources);

banner.vue

advManager.requestAd(bannerID).then((result) => {
  if (result) {
    this.bannerContent = result;
    this.showBanner = true;
  }
});

解析-单例模式
advMaster.js中，通过const advInstall = new (class {…})()实现单例。
单例模式的目标是确保一个类只有一个实例，并提供一个全局访问点来访问该实例。
这个代码片段是一个立即执行的类表达式，会在代码加载时执行一次。
这意味着它会创建一个实例并赋值给 advInstall 变量，然后这个实例就会一直存在于应用程序的内存中。

普通类创建的方法例子
调用可反复创建实例，不是同一个。

export class AdvInstall {
  constructor() {
    this.sourceList = [];
    this.pendingPromise = null;
  }

  initialize(sources) {
    this.sourceList = sources;
  }

  requestAd(id) {
    return new Promise((resolve, reject) => {
      // Your implementation here...
    });
  }

  findAd(adList, id) {
    return (adList || []).find((ad) => ad.impid === id);
  }
}

const resources1 = ['123', '456'];
const advInstall1 = new AdvInstall();
advInstall1.initialize(resources1);
advInstall1.requestAd(id);

const resources2 = ['789', '101'];
const advInstall2 = new AdvInstall();
advInstall2.initialize(resources2);
advInstall2.requestAd(id);