synchronous dialogs flex?

how i open synchronous dialog flex? i need duty an outmost interface (javascript) open rudimentary dialog flex concentration advantage an value according symbol user clicked (ok/cancel).

so should synchronous dialog, i.e. waits until user closed dialog this.

//this duty called javascript
function onapplicationunload():boolean
{
  var result:boolean;
  outcome = showdialogandwaitforresult();
  relapse result
}

does anybody know i this? i loop waits until dialog set fall following reads outcome relapse it, nonetheless there contingency something proceed some-more glorious reusable sharp execution asynchronous calls.

edit:
unfortunately callback does work javascript duty calls onapplicationunload() itself relapse value (similar onapplicationunload() duty flex). javascript duty bound signature called horizon i can't change it. words: javascript flex contingency also synchronous.