Question

我在角度中使用了一系列承诺，我希望在链的末尾应该返回一个值：

this.calculateeventsattended = function(username) {
   var Attendees = Parse.Object.extend("Attendees");
   var User = Parse.Object.extend("User");
   var count_pres = 0
   query1 = new Parse.Query(Attendees);
   query1.equalTo("user_id",username);
   query1.equalTo("presence",true)        

   var promise = query1.count(function(count){
       count_pres = count
   }).then(function(){
       query2 = new Parse.Query(User);
       query2.equalTo("username",username);
       query2.first().then(function(object){
           alert("parse" + count_pres)
           object.set("events_attended",count_pres)
           object.save()
       })
   })
$q.all(promise)
return count_pres
}

链条承诺＆＃39;在传递返回之前未解析：在$ q.all（promise）完成之前返回count_pres。有什么想法吗？

Answer 1

我无法想象这会有用吗？这就是你如何链接承诺与如何编写异步承诺。

function chainedPromises() {
    return $q(function(resolve) {
        query
            .firstPromise()
            .then(function(firstResult) {
                return query.secondPromise(firstResult.something);
            })
            .then(function(secondResult) {
                return query.thirdPromise(secondResult.something);
            })
            .then(function(thirdResult) {
                return query.fourthPromise(thirdResult.something);
            })
            .then(function(fourthResult) {
                resolve(fourthResult);
            });
    });
}

function asyncPromises() {
    var promises = [];

    promises.push(query.firstPromise());
    promises.push(query.secondPromise());
    promises.push(query.thirdPromise());
    promises.push(query.fourthPromise());

    return $q.all(promises);
}

chainedPromises()
    .then(function(fourthResult) {
        doSomethingWith(fourthResult);
    });

asyncPromises()
    .then(function(results) {
       doSomethingWith(results); 
    });

Javascript Angular在返回结果值之前解析promise的链

1 个答案: