How to make all AJAX calls sequential?

Question

I use jQuery. And I don't want concurrent AJAX calls on my application, each call must wait the previous before starting. How to implement it? There is any helper?

UPDATE If there is any synchronous version of the XMLHttpRequest or jQuery.post I would like to know. But sequential != synchronous, and I would like an asynchronous and sequential solution.

Answer 1

You have two choices that I can think of. One is to chain them through callbacks. The other is to make the calls synchronous rather than async.

Is there a reason you want them sequential? That will slow things down.

To make the call synchronous, you'll set the async option in the Ajax call to false. See the documentation at http://docs.jquery.com/Ajax/jQuery.ajax#options (click options tab to see them).

Answer 2

Look at this: http://docs.jquery.com/Ajax/jQuery.ajax (click on the "options" tab).

But remember a synchronous call will freeze the page until the response is received, so it can't be used in a production site, because users will get mad if for any reason they have to wait 30 seconds with their browser frozen.

EDIT: ok, with your update it's clearer what you want to achieve ;)

So, your code may look like this:

 $.getJSON("http://example.com/jsoncall", function(data) {
  process(data);
  $.getJSON("http://example.com/jsoncall2", function (data) {
   processAgain(data);
   $.getJSON("http://example.com/anotherjsoncall", function(data) {
    processAgainAndAgain(data);
   });
  });
 });

This way, the second call will only be issued when the response to the first call has been received and processed, and the third call will only be issued when the response to the second call has been received and processed. This code is for getJSON but it can be adapted to $.ajax.

Answer 3

The best way you could do this is by chaining callbacks as Nosredna said. I wouldn't recommend using synchronous XMLHttpRequest as they lock your entire application.

There aren't much helper for this as far as I know, but you could do something resembling a callback FIFO.

Answer 4

You could give narrative javascript a try http://www.neilmix.com/narrativejs/doc/

I've never used it myself though. If I wanted to do this, I would setup some kind of abstraction for chaining asynchronous actions. As others have said, the synchonous version of the ajax object blocks events from being processed while it's waiting for a response. This causes the browser to look like it's frozen until it recieves a response.

Answer 5

Set the async option to false, e.g.,

$.ajax({ async: false /*, your_other_ajax_options_here */ });

Reference: Ajax/jQuery.ajax

Answer 6

Check this plugin:

• jQuery.ajaxQueue

This plugin basically helps you to manage "Ajax race conditions".

When multiple Ajax requests are made in rapid succession, the results can be returned out of order.

Answer 7

Synchronous calls aren't necessarily slower, if you have an app where AJAX calls open, posts to, then closes a socket, multiple calls to the socket don't make sense as some sockets can only handle a single connection, in which case, queuing data so its only sent when the previous AJAX call has completed means much higher data throughput.