如何在vanilla javascript中链接for循环中的promises [英] How to chain promises in for loop in vanilla javascript

问题描述

如果我正在进行如下的异步调用，如何使用promises链接它们，那么我可以按顺序执行某些操作？在这个例子中，最终发生的是 arr 将推送项目不按顺序。我更喜欢承诺的答案，但只要有效就会做任何事情

If I am doing an async call like the following, how can chain them with promises, so i can do stuff in order? In this example, what ends up happening is that arr will push the items out of order. I'd prefer an answer with promises, but anything will do as long as it works

var fbArrOfAlbumNames = ['Profile Pictures', 'Cover Photos', 'Mobile Uploads'];
var arr = [];
for(var x = 0; x < fbArrOfAlbumNames.length; x++) {
  (function(cntr) {
    FB.api('/' + fbArrOfAlbumNames[cntr] + '/photos/', {fields: 'picture,album'}, function(response) {
      arr.push(response);
    }
  })(x);
}

推荐答案

假设您的ajax调用实际上可以并行运行你只想按顺序查看结果，然后你可以宣传ajax函数并使用 Promise.all（）按顺序获得所有结果：

Assuming your ajax calls can actually be run in parallel and you just want the results in order, then you can promisify the ajax function and use Promise.all() to get all the results in order:

// promisify the ajax call
function fbAPIPromise(path, args) {
    return new Promise(function(resolve, reject) {
        FB.api(path, args, function(results) {
            if (!result) return resolve(null);
            if (result.error) return reject(result.error);
            resolve(result);
        });
    });
}

var promises = [];
for (var x = 0; x < 10; x++) {
     promises.push(fbAPIPromise('/' + fbArrOfAlbumNames[x] + '/photos/', {fields: 'picture,album'});
}
Promise.all(promises).then(function(results) {
     // results is an array of results in original order
}).catch(function(err) {
     // an error occurred
});

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