javascript - 链式 promise 强制异步

我使用诺言来获取图像的大相册，并从该相册中抽取随机样本。我设法请求了所有相册，然后将指向图像的链接推送到对象数组。

现在，我想打印出该数组，但要等到我实际填写完之后才能打印出来。每当我在末尾添加.then()时，它只会打印出初始化的空数组。

我该怎么办才能强制异步，并且仅在数组填充后才打印。 （我正在底部打印出来）

let findImagesCatalyst = new Promise(function(resolve, reject) {
    //url options
    const options = {
      url: 'https://api.imgur.com/3/gallery/hot/time/',
      headers: {
        "Authorization": "Client-ID xxxx"
      }
    };

    //inital request
    request(options, function(err, res, body) {
      //parse the response
      body = JSON.parse(body)
        //access the data in the response
      const responseData = body.data;
      //filter only those with image counts great than 50
      const largeAlbums = responseData.filter(findDumps)
        //test to see if a dump is present
      if (largeAlbums.length > 0) {
        largeAlbums.forEach(function(i) {})
        resolve(largeAlbums)
      } else {
        reject()
      }

    })

  })
  //if successful in finding a dump, then go through them and find their albumIds
  .then(function(largeAlbums) {
    let dumpIds = largeAlbums.map(index => index.id)
    return dumpIds;
  })
  //with the album/dump ids, get each of them with a new request
  .then(function(dumpIds) {
    //for each of the dumpIds create the needed url using ES6  and then request it.
    dumpIds.forEach(function(i) {
      const albumUrlOptions = {
          url: `https://api.imgur.com/3/album/${i}/images`,
          headers: {
            "Authorization": "Client-ID xxxx"
          }
        }
        //make a request to each of the albums/dumps
      request(albumUrlOptions, function(err, res, body) {
        body = JSON.parse(body)
        const responseData = body.data
          //pick one sample image from the album/dump
        let sampleImage = responseData[randomSelector(responseData.length)].link;
        dumps.push({
          "dump": i,
          'sample': sampleImage
        })

      })
    })

    return dumps;
  })

.then(function(dumps) {
  console.log(dumps)
})

最佳答案

你是第二个。然后应该返回Promise。所有（承诺的）请求

.then(function(dumpIds) {
    //for each of the dumpIds create the needed url using ES6  and then request it.
    return Promise.all(dumpIds.map(function(i) {
        const albumUrlOptions = {
            url: `https://api.imgur.com/3/album/${i}/images`,
            headers: {
                "Authorization": "Client-ID xxxx"
            }
        };
        return new Promise((resolve, reject) => {
            //make a request to each of the albums/dumps
            request(albumUrlOptions, function(err, res, body) {
                body = JSON.parse(body)
                const responseData = body.data
                    //pick one sample image from the album/dump
                let sampleImage = responseData[randomSelector(responseData.length)].link;
                resolve({
                    "dump": i,
                    'sample': sampleImage
                });
            });
        });
    }))
})

当您使用具有非常好的ES2015 +实现的node.js时，您可以（首先，通过创建“ request的承诺版本”）来简化代码（在我看来）

let requestP = (options) => new Promise((resolve, reject) => {
    request(options, (err, res, body) => {
        if (err) {
            return reject(err);
        }
        resolve({res, body});
    });
});

然后可以将其余代码重写如下

const options = {
  url: 'https://api.imgur.com/3/gallery/hot/time/',
  headers: {
    "Authorization": "Client-ID xxxx"
  }
};

//inital request
let findImagesCatalyst = requestP(options)
.then(({res, body}) => {
    //parse the response
    body = JSON.parse(body)
        //access the data in the response
    const responseData = body.data;
    //filter only those with image counts great than 50
    const largeAlbums = responseData.filter(findDumps)
        //test to see if a dump is present
    if (largeAlbums.length > 0) {
        largeAlbums.forEach(function(i) {})
        return(largeAlbums)
    } else {
        return Promise.reject();
    }
})
//if successful in finding a dump, then go through them and find their albumIds
.then((largeAlbums) => largeAlbums.map(index => index.id))
//with the album/dump ids, get each of them with a new request
.then((dumpIds) =>
    //for each of the dumpIds create the needed url using ES6  and then request it.
    Promise.all(dumpIds.map((i) => {
        const albumUrlOptions = {
            url: `https://api.imgur.com/3/album/${i}/images`,
            headers: {
                "Authorization": "Client-ID xxxx"
            }
        };
        return requestP(albumUrlOptions)
        .then(({res, body}) => {
            body = JSON.parse(body)
            const responseData = body.data
                //pick one sample image from the album/dump
            let sampleImage = responseData[randomSelector(responseData.length)].link;
            return({
                "dump": i,
                'sample': sampleImage
            });
        });
    }))
)
.then(function(dumps) {
    console.log(dumps)
});