How to Effectively Sequence Ajax Requests in Web Applications?

Sequencing Ajax Requests

In many web applications, it is common to encounter the need to iterate through a collection and issue an Ajax request for each element. While it is tempting to leverage asynchronous requests to avoid browser freezing, managing these requests effectively can prevent server overload and other potential issues.

jQuery 1.5

For jQuery versions 1.5 and higher, the $.ajaxQueue() plugin offers a straightforward solution. This plugin utilizes the $.Deferred, .queue(), and $.ajax() functions to orchestrate Ajax requests and return a promise that resolves upon request completion.

jQuery 1.4

For jQuery 1.4 users, an alternative approach involves creating a "queue" using the animation queue on an empty object. This technique ensures that Ajax requests are executed in a controlled manner, with the first request automatically initiated if the queue is not already running.

Usage Example

The following code snippet illustrates how to implement Ajax queueing using the $.ajaxQueue() plugin. It iterates through a list of elements and copies each item to a target list via Ajax requests:

$("#items li").each(function(idx) {
  $.ajaxQueue({
    url: '/echo/html/',
    data: { html: "[" + idx + "] " + $(this).html() },
    type: 'POST',
    success: function(data) {
      $("#output").append($("<li>", { html: data }));
    }
  });
});

By employing either of these approaches, developers can effectively manage the sequencing of Ajax requests, ensuring orderly execution and avoiding potential server-side issues.

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