使用Javascript：有没有更好的办法后异步数据库X数量来执行功能/ Ajax调用 [英] Javascript: is there a better way to execute a function after x amount of async database/ajax calls

问题描述

我们有一个应用程序，在某个场合中，我们需要一个ajax后发送到客户端web服务。

using Backbone.js we have an application, in which on a certain occasion we need to send an ajax post to a clients webservice.

然而，要贴的内容，是动态的，并且是由一个特定的数组决定

however, the content to be posted, is dynamic, and is decided by a certain array.

有我们需要去获取一个数据阵列中的每一个项目。

for each item in the array we need to go fetch a piece of data.

组装需要被发送聚集的对象中的数据之后。

after assembling the data that aggregated object needs to be sent.

截至目前，我有一个同步的办法，虽然我觉得这是不是最好的方法。

as of now, i have a synchronous approach, though i feel that this is not the best way.

var arrParams = [{id: 1, processed: false},{id: 7, processed: false},{id: 4, processed: false}];

function callback(data) {
    $.post()... // jquery ajax to post the data... }

function fetchData(arr, data, callback) {
    var currentId = _(arr).find(function(p){ return p.processed === false; }).id;  // getting the ID of the first param that has processed on false...

    // ajax call fetching the results for that parameter.
    $.ajax({
        url: 'http://mysuperwebservice.com',
        type: 'GET',
        dataType: 'json',
        data: {id: currentId},

        success: function(serviceData) {
            data[currentId] = serviceData;  // insert it into the data
            _(arr).find(function(p){ return p.id === currentId; }).processed = true; // set this param in the array to 'being processed'.
            // if more params not processed, call this function again, else continue to callback
            if(_(arr).any(function(p){ return p.processed === false }))
            {
                 fetchData(arr, data, callback);
            }
            else
            {
                callback(data);
            }
        },
        error: function(){ /* not important fr now, ... */ }
    }); 
}

fetchData(arrParams, {}, callback);

是不是有启动这些异步调用和执行回调，只有当所有的结果在某种程度上？

isn't there a way to launch these calls asynchronous and execute the callback only when all results are in?

推荐答案

您必须使用jQuery $。递延对象同步。看看这篇文章递延文档

You have to use JQuery $.Deferred object to sync them. Look at this article Deferred Docs

您可以用此方式使用：

$.when(
   $.ajax({ url : 'url1' }),
   $.ajax({ url : 'url2' }) // or even more calls
).done(done_callback).fail(fail_callback);

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