在异步代码块中处理的多个 ajax 延迟调用数组，后跟同步最终代码块

Question

我是 jquery 和 ajax 的新手，我正在尝试使用延迟和承诺的概念来解决我遇到的这个问题。 我想做以下事情： 调用 URL 列表并处理从 url 返回的结果。我想先并行处理结果，然后将处理后的结果结合起来给我一个最终的结果。

伪代码如下：

var deferredAjaxCalls = [];
for (var i = 0; i < jobsListLength; i++) {
    deferredAjaxCalls.push(
        $.ajax({
            url:"/myurl",
            method:"POST",
            contentType:"application/json",
            dataType:"json",
            data:mydata,
            success:function(result){
              //Some code here that is performance intensive
            } 
        });
}
$.when.apply(this,deferredAjaxCalls).done(function(){
    for (var k=0; k< arguments.length;k++){
            //combine the results of the individual results of the
            // success part of all the ajax calls and execute some more 
            //code synchronously
    } 
}).fail( function (jqXHR, status, error) {
   //Log failed status
 });

最初，我将所有代码从成功部分移到 $.when.apply() 中。但是，这导致性能非常慢，因为现在有很多密集的计算是同步执行的。所以我正在寻找一种方法来独立执行部分代码，并同步执行最后一段

我确实读过有关使用 Promise 的信息，但找不到任何示例，其中 Promise 与带有中间处理的 ajax 调用数组一起使用，然后最终在 when.apply() 块中进行同步

什么是解决这个问题的好方法？

谢谢！

Answer 1

从数组jobsList 开始，您可能想要这样的东西：

var deferredAjaxCalls = jobsList.map(function(job) {
    return $.ajax({
        url: "/myurl",
        method: "POST",
        contentType: "application/json",
        dataType: "json",
        data: mydata
    }).then(process);// where `process` is a function that accepts $.ajax's (data, textStatus, jqXHR) and returns a *single* value/object - the result of the processing. This will standardise the data delivered below by $.when() to its success handler.
});
$.when.apply(null, deferredAjaxCalls).then(function() {
    // Due to `.then(process)` above, `arguments` are guaranteed to comprise one arg per ajax call.
    // Otherwise you potentially have the problem reported here - http://stackoverflow.com/questions/12050160/
    for (var k=0; k<arguments.length; k++) {
        // Combine the results of the individual results of the success part of all the ajax calls and execute some more code synchronously.
    }
    // In this function deliver an error by returning `$.Deferred().reject(new Error('myReason'))`
    return combined_result;
}, function(jqXHR, status, error) {
    // This hander will receive multiple $.ajax() params, which are best normalised into a single Error object. 
    return new Error(status); // similar to .then(process) above, reduce $.ajax's error args to a single "reason".
}).then(null, function(err) {
    // All errors delivered by code above arrive here as a js Error.
    // But please note that, in jQuery <v3.0, any uncaught errors above will genuinely throw (to the console).
    console.log(err.message);
});

Answer 2

您可以尝试使用延迟：

  var req_responses = [];
  var deferreds = [];

  for(var i in jobs) {
     deferreds[i] = new $.Deferred();
  }

  for(var i in jobs) {
     (function(i) {
        $.ajax ({
           url: ".",
           type: "POST",
           dataType: "json",
           done: function(response) {
              //process the response
              req_responses[i] = response;
              deferreds[i].resolve();
           }
        });
     })(i);   
  }

  $.when.apply(deferreds).then(function(os) {
     //all the responses are in req_responses
     //finish processing
     alert("done");
  });