Question

var btn:Button;
if(btn != null  &&  btn.label != '') {
      mx.controls.Alert.show("d");  
}

In the above if clause, is it guaranteed that the first condition(btn != null) will
be evaluated before the second condition?

Answer 1

Yes – ActionScript performs appropriate short-circuiting for the && operator:

• http://www.adobe.com/support/flash/action_scripts/actionscript_dictionary/actionscript_dictionary013.html

So not only will it evaluate the expressions in the order you described, it won’t bother evaluating the second expression at all if the first one returns false (which is as important a detail as the order of evaluation).

Just as a note, ActionScript also supports short-circuiting the logical or operator (||).