javascript - Promise 中的 JS Promise

Question

应该在 3 次尝试中检索位置的 getLocation() 函数会返回 undefined。 navigator.geolocation.getCurrentPosition() 返回正确的位置，但问题出在 promise 处理中。

问题显然是我在 promise 内调用 promise 。我不允许在已声明为 async 的 geolocate() 中使用 await 关键字。

原始调用:

var getLocationPromise = this.getLocation();
// Do something...
location = await getLocationPromise;

getLocation():

  async getLocation() {
    return new Promise((resolve, reject) => {
      var geolocate;
      for (let i=0; i<3; i++) {

        geolocate = this.geolocate();

        try {
            var location = geolocate;//CAN'T USE AWAIT INSIDE ASYNC...
            resolve(location);
        } catch(err) {
            continue;
        }
      } 
      reject("Max geolocation attempts");
    });
  }

地理定位():

  async geolocate() {
    return new Promise((resolve, reject) => {

      navigator.geolocation.getCurrentPosition(
        (position) => {
          resolve(position);
        },
        (err) => {
          reject(err);
        },
        {enableHighAccuracy: true, timeout: 20000, maximumAge: 1000}
      );
    });
  }

Answer 1

只要以下内容在声明为异步的函数中

var getLocationPromise = this.getLocation();
// Do something...
location = await getLocationPromise;

应该没问题

查看 getLocation/geolocate，除非您需要单独的 geolocate 方法，否则它们应该能够组合并简化为

getLocation() {
    var geolocate = () =>
        new Promise((resolve, reject) => 
            navigator.geolocation.getCurrentPosition(resolve, reject, {
                enableHighAccuracy: true,
                timeout: 20000,
                maximumAge: 1000
            });
        );
    // this function will "retry" the supplied function (fn) cont times
    var limitedPromiseRetry = (fn, cont) => fn().catch(err => cont > 0 ? limitedPromiseRetry(fn, cont-1) : Promise.reject('Max number of geolocation attempts'));
    return limitedPromiseRetry(geolocate, 3);
}