如何正确处理Promise.all：获取undefined
我试图从一些对不同的REST API的请求中得到一个数组充满了信息。 我想使用Promise.all来做到这一点，但由于某种原因，它产生了一堆内部undefined的数组。
[undefined，undefined，undefined，undefined]
这是我的代码：
var _ = require("lodash");//Used exclusively to check if the result from the request is an object var ccxt = require("ccxt");//External library used to make the requests let pairs = ["ETH/EUR", "BTC/EUR", "LTC/EUR", "BCH/EUR"]; //Array on which the Promise.all is based function test(p) { for (var i = 0; i < ccxt.exchanges.length; i++) { //Looping through all the rest APIs let exchange = new ccxt[ccxt.exchanges[i]](); //Defining each API to make the requests if (exchange.hasFetchOrderBook) { exchange //Beginning of the request .fetchOrderBook(p) .then(order => { if (_.isObject(order) && order.bids[0][1]) { let now = Math.floor(new Date()); order.mkt = exchange.name; order.pair = p; order.ping = now - order.timestamp; return order; //Return the result of the request } }) .catch(e => {}); } } } Promise.all(pairs.map(test)) //Making the requests based on the Pairs Array .then(res => { console.log(res); //Logging the results ==> [undefined, undefined, undefined, undefined] for some reason... }) .catch(e => { console.log(e); });
我知道正确的请求，因为如果我console.log循环内的order ，我得到了正确的结果 – 日志logging时的结果示例：
{ bids: [ [ 12009.52, 0.0468 ], [ 12008.5, 0.0227 ], [ 12007.48, 30.9321 ], [ 12006.46, 0.0537 ], [ 12005.45, 0.0157 ], [ 12004.43, 7.1659 ], [ 12003.41, 0.0164 ], [ 12002.39, 23.4159 ], [ 12001.38, 0.0284 ], [ 12000.36, 0.0132 ], [ 11999.34, 0.0194 ], [ 11998.33, 0.0034 ], [ 11997.31, 7.526 ], [ 2445.72, 34.075 ], [ 2445.17, 25.4842 ], [ 2444.96, 0.1118 ], [ 2444.75, 23.288 ], [ 2444, 0.0247 ], [ 2443.8, 0.192 ], [ 765.51, 0.0828 ] ], asks: [ [ 12048.74, 2.523 ], [ 12049.77, 0.0159 ], [ 12050.79, 0.029 ], [ 12051.82, 0.0061 ], [ 12052.84, 0.0181 ], [ 12053.87, 0.0164 ], [ 12054.89, 0.0355 ], [ 12055.92, 0.0042 ], [ 13419.62, 0.0063 ], [ 13420.64, 0.0174 ], [ 13421.78, 0.0143 ], [ 13422.92, 0.026 ], [ 13424.06, 0.0055 ], [ 13425.2, 14.4552 ], [ 13426.23, 0.0065 ], [ 13427.25, 0.0057 ], [ 13428.39, 0.0147 ], [ 13429.53, 4.0375 ], [ 13430.56, 23.9541 ], [ 13431.58, 0.0137 ] ], timestamp: 1512845715447, datetime: '2017-12-09T18:55:15.447Z', mkt: 'LakeBTC', pair: 'BTC/EUR', ping: 0 }
所以我想我正在处理的问题与函数的asynchronous特性有关…但我不知道如何使它同步。 再次，只是为了澄清我的问题：目的是获得一个数组与4种不同types的对象（每对 – >数组），以便我可以在每个对象上操作。 为了更清楚一点，下面是我想要实现的一个例子：
[ [ Object1, Object2, Object3, etc... ], [ Object1, Object2, Object3, etc... ], [ Object1, Object2, Object3, etc... ], [ Object1, Object2, Object3, etc... ] ]
为什么是Promise.all而不是等待请求的Promise.all返回数组？
我希望这已经够清楚了！ 如果不让mw知道！ ：P
在此先感谢您的帮助！
你的test函数确实返回一个undefined 。 您需要返回结果的承诺：
function test(p) { return Promise.all(ccxt.exchanges.map(api => { //Looping through all the rest APIs //^^^^^^^^^^^^^^^^^^ let exchange = new ccxt[api](); //Defining each API to make the requests if (exchange.hasFetchOrderBook) { return exchange //Beginning of the request .fetchOrderBook(p) .then(order => { if (_.isObject(order) && order.bids[0][1]) { let now = Math.floor(new Date()); order.mkt = exchange.name; order.pair = p; order.ping = now - order.timestamp; return order; //Return the result of the request } // else undefined }) .catch(e => {}); // undefined } // else undefined })); }
当然， if条件不适用或者发生错误，你的承诺仍然满足undefined 。