[javascript] JavaScript: Global variables after Ajax requests

the question is fairly simple and technical:

var it_works = false;

$.post("some_file.php", '', function(data) {

     it_works = true;

});

alert(it_works); # false (yes, that 'alert' has to be here and not inside $.post itself)

What I want to achieve is:

alert(it_works); # true

Is there a way to do that? If not can $.post() return a value to be applied to it_works?

It seems that your problem is simply a concurrency issue. The post function takes a callback argument to tell you when the post has been finished. You cannot make the alert in global scope like this and expect that the post has already been finished. You have to move it to the callback function.

AJAX stands for Asynchronous JavaScript and XML. Thus, the post to the server happens out-of-sync with the rest of the function. Try some code like this instead (it just breaks the shorthand $.post out into the longer $.ajax call and adds the async option).

var it_works = false;

$.ajax({
  type: 'POST',
  async: false,
  url: "some_file.php",
  data: "",
  success: function() {it_works = true;}
});

alert(it_works);

Hope this helps!

The reason your code fails is because post() will start an asynchronous request to the server. What that means for you is that post() returns immediately, not after the request completes, like you are expecting.

What you need, then, is for the request to be synchronous and block the current thread until the request completes. Thus,

var it_works = false;

$.ajax({
  url: 'some_file.php',
  async: false,  # makes request synchronous
  success: function() {
    it_works = true;
  }
});

alert(it_works);