在循环中使用$ .Deferred（）和嵌套的ajax调用 [英] Using $.Deferred() with nested ajax calls in a loop

问题描述

我花了太多时间寻找类似的问题和尝试解决方案，所以我希望有人有解决方案。

I've spent far too many hours searching for similar questions and trying solutions, so I hope someone has a solution.

基本上，我希望收到通知当函数a（）完成时。问题是该函数包含一个ajax调用和一个调用b（）的循环，它再次包含一个ajax调用。

Basically, I would like to be notified when a function a() has completed. The problem is that the function contains an ajax call and a loop that calls b(), which again contains an ajax call.

使用FIDDLE更新： http://jsfiddle.net/hsyj7/1/

UPDATED WITH FIDDLE: http://jsfiddle.net/hsyj7/1/

如下所示：

// called by main()
function a() {
  return $.ajax("http://url1").pipe(function(data){
    for (var i = 0; i < 2; i++) {
      console.log('a called');
      b();
    }
  });
}

// called by a()
function b() {
  for (var i = 0; i < 2; i++) {
    $.ajax("http://url2", function(data){
      // do something
      console.log('b called');
    }
  }
}

function main(){
  $.when(a()).done(function(){
    console.log('all completed');
  });
}

我想看到的是什么是，可能同时调用顶部的a（）：

What I would like to see then is, possibly with both calls to a() at the top:

a called
b called
b called
a called
b called
b called
all completed

相反，我得到

a called
all completed
b called
b called

或其中的一些变体。

我知道以上代码缺少循环和b（）中的延迟功能。
在我尝试的一些变种中，main（）中的done（）处理程序永远不会被调用。

I am aware that the above code is missing defer functionality in both the loop and in b(). In some of the variants I have tried, the done() handler in main() is never called.

任何人都知道怎么做？

推荐答案

是的，使用延期是这样做的方法：

Yeah, using Deferred is the way to do that:

function a() {
    var def = $.Deferred();

    $.ajax("http://url1").done(function(data){
        var requests = [];

        for (var i = 0; i < 2; i++) {
             requests.push(b());
        }

        $.when.apply($, requests).then(function() { def.resolve(); });
    });

    return def.promise();
}

// called by a()
function b() {
    var def = $.Deferred(),
        requests = [];

    for (var i = 0; i < 2; i++) {
        requests.push($.ajax("http://url2").done(function(data){
            // do something
            console.log('b called');
        });
    }

    $.when.apply($, requests).then(function() { def.resolve(); });

    return def.promise();
}

function main(){
    $.when(a()).done(function(){
        console.log('all completed');
    });
}

//编辑：用<$ c替换 .pipe $ c> .done 。

// Replaced .pipe with .done.

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