同时进行多个AJAX调用和连续进行它们之间有区别吗？

Question

I am using jQuery, and jQuery Mobile to make a mobile app, if that matters that much.

My question is, is it better practice to perform multiple AJAX calls one way or the other?

For example, having a variable that counts all the ajax calls, and then if that variable maxes out, call the complete function such as:

var count = 0
$.ajax({
    //stuff
}).done({
    count++;
    if(count == 5){
        complete();
    }
});
...

or is it better to run them in a chain like:

$.ajax({
    //stuff
}).done({
    $.ajax({
        //stuff
    }).done({
        $.ajax({
            //stuff
        }).done({
            //do complete stuff
        });
    });
});

The application is that multiple API calls need to be made to gather all the information necessary and then manipulate something afterwards. Is there a difference performance wise and is there a "best practice"?

Answer 1

Do what's best for your application. If you have multiple independent sets of data to fetch and you don't rely on data from one set before fetching the other, then by all means request all of them simultaneously. Let the browser worry about throttling them.

Also, don't use your counting method to make sure they all finished. jQuery returns a handy Deferred object with AJAX requests. Untested and simplified, but this should get you started:

$.when (
  $.ajax('/data1'),
  $.ajax('/data2'),
  $.ajax('/data3')
).done(function (data1, data2, data3) {
  console.log(arguments);
});

See also:

• http://api.jquery.com/jquery.when/
• http://api.jquery.com/category/deferred-object/
• https://stackoverflow.com/a/4878978/362536