Observe variable >> need to get "on change event"

you're using javascript ?

yes I do

use setTimeout to call a function every N seconds. in that function check the values of the boolean variable. if it changes show an alert

http://www.techiwarehouse.com/cms/engine.php?page_id=3e7a2280

have a look at the above url for example

thanks a lot.
but I'm more searching for something like event.observe(element,"change",function(){...});
the problem is that in DOM2 there is no eventname "change" for a variable, just for form elements.

You need the watch method, but is not cross- browser compatible (as far as I know):
http://www.devguru.com/technologies/ecmascript/quickref/watch.html

thanks for the response. well I need a cross-browser solution so the Observer part looks in general fine but not for my requirement, cause class A sets the value on its own

class A {
public boolean watchme = false;
}

class B {
// if A.watchme changes to true then dosomething
}

Thank you all very much  for your responses.
At the end I used Warpseh's solution slightly modified.