在 ios 离子应用程序中使用 javascript 承诺

Question

我需要在 ionic 中使用以下承诺（ios 显然在 android 上没问题）：

var Attendees = Parse.Object.extend("Attendees");

    return Promise.all(eventDetails.map(detail => {
        return Promise.all([new Promise((res, rej) => {
            var query2 = new Parse.Query(Attendees);
            query2.equalTo("event_id", detail .id_event);    
            query2.count({
                success: function(number) {
                    detail["n_requests_received"] =  number;
                    alert("received")
                    res('Some value if required'); //These are needed or promise chain will hang
                }
            });
        }),
        new Promise((res, rej) => {
            var query3 = new Parse.Query(Attendees);
            query3.equalTo("event_id", detail .id_event);
            query3.equalTo("status", "confirmed")
            query3.count({
                success: function(number) {
                    detail["n_requests_confirmed"] =  number;
                   // alert("confirmed")
                   res('Some value if required'); //These are needed or promise chain will hang
                }
            });
        })]);
    }));

你知道怎么做吗？

Answer 1

我使用 deferred 是为了让你可以运行一个 Promise 链，而不是将它们分开。如果调用发生错误，您还需要处理错误情况（两个 Promise 使用相同的错误函数）。它会正确地拒绝承诺，以便您妥善处理。

var promises = [];

eventDetails.forEach(function(detail) {
    var deferred = $q.defer();

    new Parse.Query('Attendees')
    .equalTo("event_id", detail.id_event) 
    .count().then(function(number) {
        detail["n_requests_received"] =  number;
        alert("received");
        return new Parse.Query('Attendees')
        .equalTo("event_id", detail .id_event)
        .equalTo("status", "confirmed")
        .count();
    }).then(function(confirmedCount) {
        detail["n_requests_confirmed"] = confirmedCount;
        deferred.resolve('I have resolved this promise');
    }, function(err) {
        console.error(JSON.stringify(err));
        deferred.reject('Error: ' + JSON.stringify(err));
    });

    promises.push(deferred.promise());
});

$q.all(promises).then(function(res) {
    // completed all promises w/ no errors
}, function(err) {
    console.error(JSON.stringify(err));
});