On Oct 20, 5:37*pm, sheldonlg <sheldonlgwrote:
(..)
The problem is that the AJAX call does not complete before the test.
So, I put in a delay after the call to the AJAX function. *I even tried
5000 msec. *Meanwhile, I looked at the value of the hidden variable
using Firebug. *What happens is that the variable does not change until
the delay is completed and the value that the function obtains is the
old value.
It seems as if the AJAX call does not complete until after the delay.
Why would this be so? *Shouldn't the AJAX functionality complete while
in the delay?
Yes but no. The XHR request completes but no callback can be called
because you've got JS stuck into a loop. The Golden rule is: *never*,
under no circumstances will two things happen at the same time in JS,
because it's single-threaded. (and being single threaded is a Good
Thing, BTW).
For the delay, I an using a brute force while loop -- so there is no
setInterval problem here.
Don't use loops for timing, it's a nonsense. Nothing else, nothing but
the loop can/will happen in the browser during a loop. It's as
freezing the time. Read the FAQ.
So, how can I do this sequence?
1 - Call AJAX which sets the hidden variable.
2 - Delay
3 - Get the changed value
JS is single threaded so nothing else can happen since you are
throwing it into a brute-force while loop...
To check that/if something has happened every once in a while inline
something like:
(function () {
if (hasHappenedAlready) {
doWhatYouWantedToDo();
} else {
//keep waiting
setTimeout(arguments.callee, 100); //check again in 100ms.
}
})();
But you could as well have used a *synchronous* XHR call instead.
--
Jorge.
