Is Ajax implemented correctly in Firefox? Synchronous problem

Question

Please take a look at the following code, what do you think will be the first magazine to be printed?
In Chrome and IE, "sync ajax call: success" first appears, which is expected
BUT in FF (tested in FF 3.6 and FF 17.0) instead shows "an asynchronous ajax call: success", which means that we make the second as a synchronous call, but when its onreadystatechange is started, the asynchronous (first) ajax call handler was made earlier than the synchronous (second) ajax call, does it make sense?
Isn't that a firefox bug?

// first ajax call, Note: this is asynchronous. $.ajax({ url: "/rest/someUrl", async : true, dataType : "json", contentType: "application/json", success : function(data) { console.log("async ajax call: success"); }, error : function(data) { } }) // second ajax call, Note: this is synchronous. $.ajax({ url: "/rest/someUrl", async : false, dataType : "json", contentType: "application/json", success : function(data) { console.log("sync ajax call: success"); }, error : function(data) { } }) 

Answer 1

to implement something "correctly", there must be some kind of specification.

Inside the specification, I did not find a reference to the fact that all scripts should stop executing before the synchronous request is complete (note that async-XHR is already running when sync-XHR starts).

But I found this:

• Each XMLHttpRequest object has its own task source. Namely, the source of the XMLHttpRequest job.
  - both requests represent the same source-source -

• When the user agent must queue a task, it must add the specified task to one of the task queues of the corresponding event loop. [...] tasks from different sources of tasks can be placed in different task queues.
  - both tasks can be added to the same task queue, but should not -

• An event loop must be continuously executed using the following steps as long as it exists:
  1. Run the old task in one of the queues of the tasks of the event loop, if any, [...]. The user agent can select any task queue.
  - he now selects a task queue where he puts a synchronous request

When I do not understand this wrong, and my logic is not wrong, this can happen:

Firefox puts both XHRs in the same queue, IE and Chrome put them in different task queues.

All browsers now start the task queue, where they host the synchronous XHR.

• In IE and Chrome, synchronous XHR is the oldest task in its lineup and runs
• In FF, asynchronous XHR is the oldest in its lineup and runs

Both implementations seem correct.