ActionScript 2.0 Language Reference - Adobe Help and Support

if (shouldExecute == true) {
trace("your statements here");
}
// true is also implied, so the if statement could also be written:
// if (shouldExecute) {
// trace("your statements here");
// }
The following example shows how automatic data typing converts true to the number 1:
var myNum:Number;
myNum = 1 + true;
trace(myNum); // output: 2
See also
false constant, Boolean
undefined constant
A special value, usually used to indicate that a variable has not yet been assigned a value. A
reference to an undefined value returns the special value undefined. The ActionScript code
typeof(undefined) returns the string "undefined". The only value of type undefined is
undefined.
In files published for Flash Player 6 or earlier, the value of String(undefined) is "" (an
empty string). In files published for Flash Player 7 or later, the value of String(undefined)
is "undefined" (undefined is converted to a string).
In files published for Flash Player 6 or earlier, the value of Number(undefined) is 0. In files
published for Flash Player 7 or later, the value of Number(undefined) is NaN.
The value undefined is similar to the special value null. When null and undefined are
compared with the equality (==) operator, they compare as equal. However, when null and
undefined are compared with the strict equality (===) operator, they compare as not equal.
Availability: ActionScript 1.0; Flash Player 5
Constants 41