完成两个ajax请求后执行回调的最简单方法

问题描述：

我有一个充当API的Node.js应用程序.我收到一个请求，该请求基于我对另一台服务器执行一些ajax请求，缓存结果并将结果发送回客户端的操作.

I have a Node.js application that functions as an API. I get a request, based on the action I perform some ajax request to another server, cache the results, and send the results back to the client.

现在对于这个新请求，我需要执行两个单独的ajax调用，并在两个都完成时向客户端做出响应.为了加快处理速度，我不想将它们嵌套.

Now for this new request I need to do two separate ajax calls, and give a response to the client when both of them are finished. To speed things up I do not want to nest them if that is possible.

此外，这些ajax请求非常棘手，有时服务器会浪费我们的时间，或者返回不好的结果，在这种情况下，我递归地执行相同的ajax请求.

Also, these ajax request are tricky, in the way that sometimes the server times our, or give bad results back, in that case I recursively do the same ajax request.

答

好的，诺言使这个琐碎的事情变得如此:

Well, promises make this trivial:

 var http = Promise.promisifyAll(require("http"));
 Promise.all(["url1","url2"]).map(getWithRetry).spread(function(res1,res2){
      // both responses available
 }).catch(function(err){
      // error handling code
 });

带有承诺的 getWithRetry 的示例可以是:

An example of getWithRetry with promises can be something like:

function getWithRetry(url){
      return http.getAsync(url).catch(function(err){ 
           return http.getAsync(url); // in real code, check the error.
      });
}

但是，您没有使用它们，因此必须手动进行同步.

However, you're not using them, so you have to manually synchronize it.

 var res1,res2,done = 0;;
 requestWithRetry("url1",function(err,result){
       if(err) handleBoth(err,null,null);
       res1 = result;
       done++;
       if(done === 2) handleBoth(null,res1,res2);
 });
  requestWithRetry("url2",function(err,result){
       if(err) handleBoth(err,null,null);
       res2 = result;
       done++;
       if(done === 2) handleBoth(null,res1,res2);
 });
 function handleBoth(err,res1,res2){
     // both responses available here, the error too if an error occurred.
 }

关于重试，它可以是 requestWithRetry 本身的一部分，后者应仅检查 err 在回调中是否为null，如果是，则重试一次或两次(取决于您的期望行为).

As for retrying, that can be a part of requestWithRetry itself, which should just check if err is not null in the callback, and if it is, retry once or twice (depending on your desired behavior).

完成两个ajax请求后执行回调的最简单方法

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