NodeJs forEach 请求承诺在返回之前等待所有承诺

Question

问题是我无法兑现对 return 任何事情的承诺。他们..只是空着。

我在 SO 上看到的每个答案都告诉我这样做，尽管由于某种原因这不起作用。我束手无策，拉头发，砸键盘；有人能指出我的愚蠢之处吗？

var q = require('q');
var request = require('request-promise'); // https://www.npmjs.com/package/request-promise

function findSynonym(searchList) {
    var defer = q.defer();
    var promises = [];
    var url = "http://thesaurus.altervista.org/service.php?word=%word%&language=en_US&output=json&key=awesomekeyisawesome";
    var wURL;
    searchList.forEach(function(word){
        wURL = url.replace('%word%',word);
        promises.push(request(wURL));
    });

    q.all(promises).then(function(data){
        console.log('after all->', data); // data is empty
        defer.resolve();
    });

    return defer;
}
var search = ['cookie', 'performance', 'danger'];

findSynonym(search).then(function(supposedDataFromAllPromises) { // TypeError: undefined is not a function [then is not a function]
    console.log('->',supposedDataFromAllPromises); // this never happens
});

Answer 1

所以，事实证明我正在解决承诺或其他事情。返回 q.all() 效果很好 :)

function findSynonym(searchList) {
    var promises = [];

    var url = "http://thesaurus.altervista.org/service.php?word=%word%&language=en_US&output=json&key=REDACTED";
    var wURL;

    searchList.forEach(function(word){
        wURL = url.replace('%word%',word);
        promises.push(request({url:wURL}));
    });

    return q.all(promises);

}
var search = ['cookie', 'performance', 'danger'];

findSynonym(search)
            .then(function(a){
            console.log('->',a);
        });

Answer 2

您正在 return 没有 .then 方法的 Deferred 对象 defer，而不是 Promise 对象 defer.promise.

但无论如何，那是deferred antipattern，这里没有必要使用deferreds。只是 return Promise.all 得到你的承诺：

function findSynonym(searchList) {
    var url = "http://thesaurus.altervista.org/service.php?word=%word%&language=en_US&output=json&key=awesomekeyisawesome";
    var promises = searchList.map(function(word) {
        return request(url.replace('%word%', word));
    });
    return q.all(promises).then(function(data){
        console.log('after all->', data); // data is empty
        return undefined; // that's what you were resolve()ing with
    });
}

NodeJs forEach 请求承诺在返回之前等待所有承诺

NodeJs forEach request-promise wait for all promises before returning

javascript

get

node.js

promise